Top Stories of 2015 from Photonics.com

Flexible Film Creates Colors from Reflected Light

June 2015

A team at the University of Central Florida’s College of Optics and Photonics (CREOL) in June developed an ultrathin, color-changing film that reflects rather than emits light. This could potentially change the clothing we wear, in addition to enhancing displays.

A National Geographic photograph of an Afghan girl is used to demonstrate the color-changing abilities of the nanostructured reflective display. Photo courtesy of University of Central Florida.

The researchers created the film using a simple and inexpensive nanoimprinting technique that is able to produce a plasmonic nanostructured surface over a large area. Specifically, a thin layer of high-birefringence liquid crystal is sandwiched over a metallic nanostructure shaped like an egg carton that absorbs some light wavelengths and reflects others. The colors reflected can be controlled by voltage applied to the liquid crystal layer. Interaction between liquid crystal molecules and plasmon waves on the nanostructured metallic surface play a key role in generating the polarization-independent, full-color tunable display.

The research is ongoing, according to professor Debashis Chanda of the university’s NanoScience Technology Center at CREOL, thanks to funding from the National Science Foundation; the funding is meant to assist the team in solving and gaining a better understanding of areas such as angular response, development of flexible architecture, and incorporation of black state. Chanda and his colleagues said recently that they are now examining “viewing angle-dependent color generation, gray state, etc.,” and are working to “scale up the process to fabricate 4 × 4 in. displays.”

As a step toward bringing the ultrathin film to the commercial market, the researchers have established e-Skin Displays Inc. The company plans to “develop low power reflective displays for wearables, pico projectors, signage/bill boards, etc.,” Chanda said.

Smartphone Microscope Counts Parasites in Blood

May 2015

A new mobile phone microscope, introduced in May by engineers at the University of California, Berkeley (in conjunction with the National Institute of Allergy and Infectious Diseases and collaborators from Cameroon and France), is capable of analyzing blood, ultimately allowing health providers to obtain critical information in the field. The primary purpose of the device is to automatically detect and quantify bodily infection caused by parasitic worms.

The next generation of UC Berkeley’s CellScope technology, called CellScope Loa, the microscope could help revive efforts to eradicate debilitating diseases in Africa, and elsewhere.

“We previously showed that mobile phones can be used for microscopy, but this is the first device that combines the imaging technology with hardware and software automation to create a complete diagnostic solution,” said Daniel Fletcher, an associate chairman and professor of bioengineering at UC Berkeley whose lab pioneered the CellScope. “This research is addressing neglected tropical diseases.”

A pilot study was conducted in Cameroon, where health officials have been battling onchocerciasis (river blindness) and lymphatic filariasis, both of which are caused by parasitic worms. Using motion instead of molecular markers or fluorescent stains to detect the movement of worms, the researchers found that the video CellScope was as accurate as conventional screening methods.

Control of the device is automated through a proprietary, purpose-specific app developed by the researchers. The phone communicates wirelessly to controllers in the base to process and analyze the blood sample. Gears move the sample in front of the camera, and an algorithm automatically analyzes the telltale “wriggling” motion of the worms from the phone’s captured video. The worm count is then displayed on the screen.

According to information from Fletcher’s Development Impact Lab, the researchers are now evaluating hand-held instruments, which are “smaller, simpler, more reliable and significantly cheaper than their predecessors,” in a large-scale “test-and-treat” pilot study in Cameroon that will involve 30,000 to 60,000 patients.

Perovskite Nanowires Yield Efficient, Tunable Lasers

April 2015

Growing nanowires has been found to produce tunable lasers with nearly 100 percent efficiency. The technique, developed by a team at the University of Wisconsin-Madison, created single-crystal lead halide perovskite nanowires, which possess low lasing thresholds and Q factors around 3600.

“We have developed an extremely simple method to grow [perovskite compounds] into elongated crystals that make extremely promising lasers,” said Song Jin, a chemistry professor at UW-Madison, adding that the new technique is cheaper and skips the complicated equipment needed to make conventional lasers.

Unsorted nanowire crystals immediately after production. Photo courtesy of Song Jin/University of Wisconsin-Madison.

The nanowires grow in about 20 hours once a glass plate coated with a solid reactant is submerged in a solution of a second reactant. Simple changes to the recipe can produce nanowires with different emission wavelengths in the visible spectrum.

Now, the researchers are expanding the lead halide perovskite material families, demonstrating lasing from other analogous materials.

“The newer materials show enhanced photostability and thermal stability under illumination and lasing conditions. We have also further expanded the wavelength tunability such that we can now get lasing continuously from 490 to about 824 nm,” Jin said.

His team is working on fabricating efficient, stable LED devices, as well, which would be “first based on such single-crystal perovskite nanostructures.” This will push the research toward electrically driven lasing devices that could “truly enable the practical applications of this technology in photonics, optical communications, sensors and other miniaturized devices.

Solar Sail Spacecraft Begins Test Voyage in Orbit

May 2015

May 20 marked the beginning of testing of The Planetary Society’s LightSail, a device made to sail on sunlight that the organization says could change how satellites, or even larger spacecraft, move around the solar system. LightSail, packaged into a CubeSat — “tiny spacecraft often hitch rides to orbit aboard rockets carrying bigger payloads,” according to The Society (http://sail.planetary.org) — was launched into space aboard a United Launch Alliance (ULA) Atlas V rocket for about a month. During that time, scientists observed the small spacecraft deploy large, reflective solar sails measuring 32 m².

“The test mission has been a high-intensity, high-profile dress rehearsal,” said Jennifer Vaughn, chief operating officer for The Planetary Society.

The Planetary Society’s LightSail, packaged into a CubeSat, successfully completed its first test mission in June, during which it deployed large, reflective solar sails. A second LightSail flight is set for fall 2016. Photo courtesy of The Planetary Society.

LightSail did not get high enough above Earth’s atmosphere for “solar sailing,” but the challenging mission still allowed scientists to study the sails’ behavior.

“This LightSail test taught us a lot, just as we hoped it would, and so we’re ready to do some real solar sailing with LightSail’s 2016 mission,” said Bill Nye, CEO of The Planetary Society. “We’re changing the way humankind explores space.”

Right now, the Society is starting a testing and integration process for both LightSail and its partner spacecraft, Prox-1. Specifically, scientists will “test individual components, perform final assembly of the spacecraft, and then complete final system-level testing before handing the integrated LightSail and Prox-1 unit over to the [U.S.] Air Force Research Laboratory in Albuquerque, N.M.,” according to Jason Davis, digital editor for The Planetary Society. During final system testing, both Prox-1 and LightSail will be placed on the vibration table and into a thermal vacuum chamber to make sure they are ready for the space environment. Davis noted, “So far, so good on all tests.”

“We’re ramping up for our second [LightSail] flight in fall 2016 aboard a SpaceX Falcon Heavy rocket,” he said. “This time, we’ll fly high enough to escape most of Earth’s atmospheric drag and demonstrate actual solar sailing, raising our orbit by about a kilometer per day.”

This second mission will last about four months. Davis said there are no official plans beyond this, but NASA is “watching and collaborating on the project closely because they’re flying a similar solar sailing mission to a near-Earth asteroid in 2018.”

‘Flat Lens’ Masters Chromatic Aberration

February 2015

A new achromatic metasurface — able to bend different wavelengths of light by the same amount — was shown in February to overcome limitations of earlier flat optics. The ultrathin “flat lens,” developed by a team at Harvard University, is composed of a glass substrate and nanoscale silicon optical antennas. These antennas can be designed to manipulate how light passing through the lens is diffracted, potentially allowing the metasurface to generate a perfectly focused image or a twisting vortex beam.

Several years ago, the researchers, led by Harvard professor Dr. Federico Capasso, were able to demonstrate a prototype lens that corrected for some of the aberrations of conventional lenses, but would only focus light of a single wavelength. The new model that Capasso’s team developed this year employs a dielectric rather than a metal for the nano-antennas, a change that improves its efficiency and, combined with a new design approach, enables operation over a broad range of wavelengths.

The new technique can also create two kinds of flat optical devices. One that deflects three wavelengths of light by the same angle, and another that can focus the three wavelengths to the same point.

“What this now means is that complicated effects like color correction, which in a conventional optical system would require light to pass through several thick lenses in sequence, can be achieved in one extremely thin, miniaturized device,” Capasso said.

Harvard’s Office of Technology Development has filed for a provisional patent for the new optical technology and is actively pursuing commercial opportunities.

“[We’re working on] lots of exciting new stuff!” Capasso said.

Light’s Wave-Particle Duality Visualized

March 2015

Light acts as both a wave and a particle.Conventionally, scientists have only been able to observe them one at a time. However, in March, a new technique was unveiled that allows the capturing of images of both properties simultaneously via the ultrafast energy-filtered transmission electron microscope from the Swiss Federal Institute of Technology in Lausanne (EPFL). Specifically, the interaction between one electron and a discrete number of photons was imaged, according to EPFL professor Dr. Fabrizio Carbone.

Energy-space photography of light confined on a nanowire simultaneously shows both spatial interference and energy quantization. Photo courtesy of Fabrizio Carbone/EPFL.

“On the energy axis of the image, each peak corresponded to the NET exchange of energy between one electron and one or two or three [or more] photons,” he said. “However, considering, for example, the peak corresponding to the exchange of one quantum, or one photon, one cannot distinguish between a process in which one only photon is absorbed, or in which three photons are absorbed and two emitted. Both these processes end up giving the same energy exchange.”

The technique was developed by a team from EPFL in collaboration with Lawrence Livermore National Laboratory and Trinity College in Connecticut. As reported in March, the actual experiment used a laser pulse to create standing waves of surface plasmon polaritons on a single nanowire that is suspended on a graphene film. The electrons interacted with the confined light on the nanowire and either sped up or slowed down. Carbone said that this experiment has demonstrated that quantum mechanics (and its paradoxical nature) can be imaged directly.

Now, to obtain more revealing images of quantum mechanics at work, the researchers are designing a new experiment.

“By substituting the direct space coordinate with its reciprocal space equivalent, all these processes can be separated,” Carbone said. “In a few words, we believe that we can obtain a new image in which not only quantization and interference can be visualized, but the interaction between single electrons and single photons can be resolved.”

Photonics Education: Where is Everybody?

September 2015

Students looking to enter the photonics field are completing programs, a number of which are at two-year community colleges, with a solid footing in optics concepts and practical skills for operating and maintaining technologies such as lasers and electro-optical systems. While the programs are often tailored to the needs of companies in their regions, many graduates undergo a year or more of on-the-job training to become proficient in the field.

In 2012, student John-Kevin Frazee demonstrated how an argon-krypton laser can be used in light shows. Photo courtesy of Central Carolina Community College.

According to the National Center for Optics and Photonics Education (OP-TEC), there are about 30 two-year colleges in the U.S. offering active photonics technology education programs. And although these tout hundreds of graduates each year, there are hundreds more vacant jobs in the field nationwide. This problem of finding enough workers is exacerbated by some colleges abandoning photonics education altogether.

Now, OP-TEC is seeking additional assistance from the National Science Foundation’s Advanced Technological Education (ATE) program, which will help colleges to update curriculum materials and boost photonics enrollment.

Drug Fluoresces, Kills Cancer Under 1 Wavelength

January 2015

A combined imaging and phototherapy technique could help guide surgeons removing chemotherapy-resistant tumors and kill any cancer cells the surgeons miss. Researchers from Oregon State University (OSU) developed the method, which they announced in January.

In their study, the new technique was shown to prevent cancer recurrence in the ovaries of laboratory mice 25 days after treatment, and the mice showed no apparent side effects or weight loss following the procedure. Specifically, the technique involves nanoparticles that contain the compound silicon naphthalocyanine, which fluoresces when exposed to near-infrared light. In addition to highlighting cancerous tissue, the drug also generates cancer-killing reactive oxygen species when illuminated. The silicon naphthalocyanine was irradiated at 785 nm with a laser power density starting at 0.3 W/cm².

At power densities up to 1.3 W/cm², the drug also gave off heat, the researchers said, showing it could be useful for photothermal therapy, as well. Meanwhile, the compound continued fluorescing during the phototherapeutic procedure and was not photobleached.

Naphthalocyanine is not water-soluble and can aggregate in the body, making it difficult (or potentially impossible) to find its way through the circulatory system and reach strictly cancer cells. To overcome this problem, the researchers earlier this year originally used a dendrimer — a water-soluble polymer and extremely tiny nanoparticle — which they said allows the napthalocyanine “to hide within a molecule that will attach specifically to cancer cells, not healthy tissue.”

Now, the researchers have developed a new technique that employs a copolymer, PEG-PCL, as a biodegradable carrier; this is an alternative to the dendrimer-based system the researchers introduced earlier this year. This new technique causes the silicon naphthalocyanine to “accumulate selectively in cancer cells and reach a maximum level in them after about one day,” according to information from OSU about these latest developments. At that point, surgery and phototherapy treatments could be done.

“We’ve now developed an improved formulation that’s biodegradable, simple, robust and reproducible,” said Olena Taratula, a research assistant professor at the OSU Oregon Health and Science University College of Pharmacy.

Taratula noted that this newer system is highly efficient. “A single-agent based system is simple and very good at targeting only cancer tumors and should significantly improve outcomes.”

Next, the team plans to test their technique on live dogs that have malignant tumors before progressing to human trials.

Reinvented Optical Gyroscope Smaller, More Sensitive

April 2015

Optical gyroscope technology could prompt an increase in sensitivity for such devices, while shrinking them to about 10 µm in size.

Researchers at the City University of New York (CUNY) and Yale University demonstrated this ability in April, showing that far-field emission patterns of light can interact strongly with rotating microdisk optical cavities. The findings present an alternative to current optical gyroscopes, which are limited by their dependence on the Sagnac effect. This phenomenon creates a measurable interference pattern when light waves split and then recombine after leaving a spinning system.

Schematics showing the far-field emission pattern of a microdisk cavity changing from symmetric to strongly asymmetric. Two cameras on the right monitor the change. Photo courtesy of Dr. Li Ge/Graduate Center and Staten Island College, CUNY .

The new optical gyroscope works by pumping light waves into an optical cavity; it then begins travelling in both clockwise and counterclockwise directions. By carefully designing the shape of the optical cavity, the researchers can control where both waves exit. Based on these developments, gyroscopes could be made small enough to be integrated into circuit boards, according to the researchers. Currently, such devices are baseball- to basketball-sized, and operate on different principles relating to the Sagnac effect — a phenomenon that creates a measurable interference pattern when light waves split and then recombine upon leaving a spinning system — one kind uses an optical cavity to confine light, while the other uses an optical fiber to guide light.

At this point, Dr. Li Ge, a professor at CUNY’s Graduate Center and Staten Island College, said he and fellow researchers are considering experimental realization. Ge added that the team would like to design a proof-of-concept demonstration to, in part, secure funding to further the research.

“We expect to perform further numerical modelings to optimize the design and address practical issues such as the precision of fabrication, selective excitation of the desired optical mode(s), packaging the microcavity with on-chip optical detectors, etc.,” Ge said. “Once we come up with an optimal design and perform the proof-of-concept experiment, we will explore commercializing the technology.”

JDSU Reveals Spinoff Names: Lumentum and Viavi

February 2015

JDSU divided into two new companies in February — Lumentum Holdings Inc. and Viavi Solutions Inc. The change became official this fall.

Specifically, JDSU’s communications and commercial optical products (CCOP) business is now Lumentum Holdings Inc. The company will develop optical components and subsystems for the data communications market, as well as lasers for both macro and micro materials processing applications. It will focus on growing its 3D sensing and commercial lasers business and expanding into other market segments that can benefit from optical and laser technologies.

Alan Lowe will lead Lumentum as chief executive officer, alongside new CFO Aaron Tachibana.

The JDSU network enablement (NE), service enablement (SE), and optical security and performance products (OSP) businesses have been renamed Viavi Solutions Inc.; Tom Waechter will lead this company.

Current JDSU stockholders will own shares in both corporations following the separation.

Since the Aug. 1 spinoff from JDSU, Lumentum’s “trajectory as a stand-alone company is on pace with our expectations,” said Greg Kaufman, director of communications for the new company. He added that Lumentum is working to advance laser and optical technologies, and is also committed to “supporting the telecom and datacom industries for the deployment of 100G for datacenter buildouts.”

Viavi’s establishment has fallen into place, as well, according to the company. As a stand-alone, Viavi’s leadership is now more focused on executing against specific goals, driving further innovation in its product portfolio and into new markets.

“The separation enables us to stay ahead of the accelerating pace of technological advances in both the networking industry, as well as those served by our Optical Security and Performance product divisions,” said a company spokesperson.

Those at Viavi also said they are excited for the future, as they work closely with customers to meet specific needs.

“What sets us apart is the ability to deliver a 360-degree view across entire network and service ecosystems,” according to the company. “We’re going to continue working closely with our customers to hear how their needs are evolving so we can tailor our solutions accordingly. We can do this now with much higher agility and focus now that Viavi is a stand-alone company focused on our primary markets.”