DISPLAYS

Toward Sharper Photos in Low Light

A diffractive filter and computational optics could boost smartphone camera sensitivity

The smartphone camera is a miracle of miniaturization and technology. But even these cameras don’t perform that well in low-light situations, in which the images captured can be dark, uneven and grainy.

“Low-light photography is not quite there yet,” says Rajesh Menon, a professor of electrical and computer engineering at the University of Utah (USA). And, along with grad student Peng Wang, Menon has proposed a way to fix that: a transparent, diffractive color filter for the camera, and computational optics to back out the true colors from the diffracted filter signal (Optica, doi: 10.1364/OPTICA.2.000933). Each pixel in the sensor array is overlain by a unit cell of a transparent filter array that diffracts incident light into an intensity pattern on the sensor. The pixel color for the final image is then backed out through a computer algorithm.

A big advantage of the system for low-light situations is that it allows substantially more light to get to the image sensor; Wang and Menon say their experiments revealed that the sensitivity can be enhanced by a factor as high as 3.12 times. The filter also should be easy to manufacture, according to the team, as it’s fabricated with standard grayscale lithography and imprinting techniques.

In addition to smartphones, the technology could also have applications in single-shot hyperspectral imaging, drones and self-driving cars. —Stewart Wills

www.osa-opn.org/news/pixel_color



QUANTUM

"Two-for-One" Fission for Solar Cells

An international team of scientists has observed how certain organic molecules can split a single photon into two molecular excitations—a quantum-mechanical process that could boost the efficiency of future solar cells (Nature Chem., doi: 10.1038/nchem.2371).

Researchers in the Cavendish Laboratory at the University of Cambridge (U.K.) used ultrafast laser pulses to study the creation of spin-triplet excitons through a process called singlet fission. The group prepared films containing derivatives of pentacene, a material known to undergo singlet fission, and subjected the samples to 2-D electronic photon echo spectroscopy. The high time-resolution of this spectroscopic technique allowed the researchers to tease out the intermediate states in the quantum process.

Among their findings, the researchers learned that the vibrational modes of the molecules create brief superposed states of a singlet exciton and a triplet exciton pair. The triplet excitons had been “dark” to previous observational techniques, but the laser spectroscopy revealed their weak signature. —Patricia Daukantas

www.osa-opn.org/news/fission



LASERS

Toward Portable Particle Accelerators?

Researchers at the University of Maryland’s Institute for Research in Electronics and Applied Physics (USA) announced a breakthrough in electron acceleration that they suggest could enable truly portable particle accelerators for low-dose cancer therapy, medical imaging and isotope production (Phys. Rev. Lett., doi:10.1103/PhysRevLett.115.194802). The technology involves the use of record-low-energy ultrashort laser pulses to accelerate electrons in a hydrogen plasma to nearly the speed of light.

Laser pulses drive a plasma wake in a jet of cold hydrogen, generating a relativistic electron beam with energies of two to 12 MeV (see image). Associated with the electron beam are the ultrashort flashes of light that contain as much as three percent of the initial pulse energy, which is much more efficient than previous studies produced. Furthermore, the technique uses only millijoules of energy, which is much less energy than previous studies required. —Valerie C. Coffey

www.osa-opn.org/news/plasma_wake



MATERIALS

Near-Perfect-Absorption Metasurfaces

Spectrally selective light absorbers are used in a wide range of advanced photonic applications—but producing large-area metasurfaces for near-perfect absorption has been an expensive proposition. A team of scientists from Duke University (USA) has now reportedly come up with a simple, scalable chemical technique for creating such metasurfaces, using deposition of silver nanocubes atop a layered metal-polymer foundation (Adv. Mater., doi: 10.1002/adma.201503281). The result, according to the team, is “truly macroscopic,” near-perfect-absorption metasurfaces that are tunable from the visible to the near-infrared. 

The combination of precise spectral selectivity and large-area fabrication could, according to the Duke researchers, make the new metasurfaces directly applicable to incorporation into imaging and photodetection technologies. They also raise the prospect of creating more active devices—such as highly sensitive infrared imaging systems—by integrating the metasurfaces with semiconductors and harvesting the “hot” electrons generated in the metal resonators to generate an electrical signal. “That’s the next step,” says postdoc and lead author Gleb Akselrod. —Stewart Wills

www.osa-opn.org/news/absorbers



INDUSTRY

SFU and Hanhai Forge "Accelerator" for Emerging Tech

Simon Fraser University (SFU), Vancouver, Canada, announced that it has signed a memorandum of understanding with the technology investment management group Hanhai Zhiye, Beijing, China, to launch a new initiative to accelerate growth and commercialization of technologies jointly developed in the two countries. The initiative, dubbed the China-Canada Commercialization and Acceleration Network (C2-CAN), has the stated goal of supporting commercialization of advanced tech originating from the two countries, as well as helping entrepreneurs and innovators to tap cross-border connections and resources.

On the SFU side, C2-CAN marks the latest step in “SFU Innovates,” a suite of university initiatives that seek to “inspire, develop, and support impact-driven innovation and entrepreneurship.” The accelerator will reside in Vancouver within the university’s VentureLabs program, which is part of a pan-Canadian accelerator network operated with two other universities.

Hanhai Zhiye focuses on science and technology park construction and development, and is seeking to “build an international science and technology service platform that hatches globally for cross-border acceleration.” Hanhai has forged accelerator and incubator partnerships in the United States and Germany, as well as five large national science and technology incubators within China itself. —Stewart Wills

GSI Group to Acquire Lincoln Laser in US$11 Million Deal

The GSI Group in Bedford, Mass., USA, a supplier of laser, precision-motion and vision technologies to original equipment manufacturers in medical and advanced industrial applications, announced an agreement to acquire ultrafast scanning equipment provider Lincoln Laser Company of Phoenix, Ariz., USA, for US$11 million in cash. Lincoln Laser’s business will integrate with the operations of Cambridge Technology, a GSI business group located in Bedford. —Valerie C. Coffey



LENSES

Flexible Fresnel Microlenses

University of Wisconsin – Madison (USA) engineer Hongrui Jian and colleagues took inspiration from the dome-shaped compound lenses of insect eyes to create tiny, flexible Fresnel lens arrays that provide a 170-degree field of view at a fraction of the size of traditional lenses (Sci. Reports, doi: 10.1038/srep15861). The Fresnel zone plates (FZPs) consist of several 0.5-mm-diameter lenses embedded in a sheet of flexible plastic. In addition to the FZPs’ flexibility, the lenses themselves are tunable—a feat not possible with rigid refractive lenses. The engineers say their FZPs could prove useful in medical imaging, contact lenses and surveillance cameras. 

They demonstrated their FZP design’s ability to provide high-resolution imaging of objects located at different axial and angular positions—including university mascot Bucky Badger and a butterfly printed on an transparency—by placing a half-cylindrical array in front of a microscope lens. Images from individual lenses were captured using a CCD camera and stitched together to produce clear, panoramic fields of view. —Sarah Michaud

www.osa-opn.org/news/microlens