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SPIE Professional January 2011

R&D Highlights

Editor’s Recommendation:
Journal of Nanophotonics

SPIE Fellow Akhlesh Lakhtakia, professor at Pennsylvania State University and editor-in-chief of the Journal of Nanophotonics, recommends “Quantum dots in biomedical applications: advances and challenges,” published online in September 2010.

Ludmila Otilia Cinteza of the University of Bucharest not only provides a succinct review of the advances made in the biomedical use of quantum dots but also discusses the challenges posed by the same nanoparticles because of their size.

Quantum dots are superior to conventional fluorophores for biomedical imaging applications because their properties can be conveniently selected by simply engineering the right size distribution. Quantum dots also appear promising for sensing pathogens as well as for treating certain forms of cancer and neural dysfunction. However, translation to clinical practice is bedeviled by their toxicity, which could persist despite encapsulation.

Quantum dots thus underscore the continued appearance of nanotechnology as a double-edged sword.

Source: Journal of Nanophotonics 4, 042503 (2010); doi: 10.1117/1.3500388.

Next generation of IR detectors

Developments in the field of both cooled and uncooled infrared detectors are paving the way toward the next generation of detectors, focal plane arrays, and associated applications for the defense and other industries.

Recent increases in demand for uncooled bolometer detectors have spurred investments from the manufacturing community, with some manufacturers now at capacities of 5000 or more units per month.

Raytheon, for instance, has moved production from small, internal fabrication lines dedicated to limited-run projects for the U.S. Department of Defense to a more open-market approach using external commercial foundries with large-scale equipment and high-capacity lines. (Proceedings of SPIE 7660, 76600X (2010); doi:10.1117/12.853675)

The move to smaller pixel pitch, such as the current industry standard of 17 μm, also enables more focal plane array (FPA) die per wafer, further enhancing yield and driving down costs. These types of economies of scale will continue to drive down market prices and open up more and more new applications.

Other developments with IR detectors include higher bolometer performance, such as a lowering of the time constant while maintaining high sensitivity. This is key to reducing the traditional bolometer Achilles heel of slow response, which leads to blur and other artifacts and limits higher-speed applications (Proceedings of SPIE 7660, 76600V (2010); doi:10.1117/12.851795).

In high-performance cooled detectors, the drive continues toward increasing format size, with some manufacturers now at 16M-pixel (4K x 4K) FPAs on a single array.

photo of Teledyne guidance sensor package
Example of Teledyne Imaging Sensors packaging: JWST Fine Guidance Sensor package for the H2RG.

New fabrication techniques allowing seamless mosaics of multiple arrays, such as reported by Teledyne Imaging Sensors (Proceedings of SPIE 7021, 70210H (2008); doi:10.1117/12.790382), can enable essentially arbitrary array sizes going forward. This enables applications such as extremely high-resolution astronomy and/or surveillance on a broad scale.

In the area of metamaterials, two interesting new developments could impact cooled detectors in the future. Both the Type II Super Lattice (T2SL) and nBn detector structures offer possible advantages over traditional semiconductor materials and are being studied intently.

For the T2SLS, data to date show these materials still have a long way to go to displace traditional semiconductor detectors (Journal of Electronic Materials 39 (7), 1030-1035 (2010); doi: 10.1007/s11664-010-1084-9), but efforts continue to achieve the performance that may be theoretically possible. The nBn detectors have been demonstrated to run at relatively elevated temperatures (relative to 77K baseline) and show promise for use in MWIR applications in the near term.

Finally, researchers from Raytheon, NASA, and DRS Sensors and Targeting Systems have reported making strides with avalanche photo diode (APD) detectors (Proceedings of SPIE 7660, 76603I, (2010); doi:10.1117/12.859186 and Proceedings of SPIE 6542, 654217 (2007); doi:10.1117/12.719358).

Previously in a niche market, these infrared detectors have the potential to dramatically improve ranges for various surveillance applications using an active laser-based approach. In particular, combining the active SWIR with the passive thermal MWIR in a single device with a single aperture significantly reduces device size, weight, and power, which can be crucial for airborne applications.

The latest developments on IR detector materials, devices, and systems will be presented in the Infrared Technology and Applications conference at SPIE Defense, Security, and Sensing in April, at SPIE Security+Defence in September, and in a special section of the SPIE journal Optical Engineering in February. Papers can be accessed through the SPIE Digital Library.

John W. Devitt serves as division chief of the remote sensing groups at Georgia Tech Research Institute.

Interest in alkali lasers

The U.S. Air Force has reported several advances in alkali lasers for future military applications.

An Air Force Research Lab press release in July reported first-light lasing from a flowing diode-pumped alkali laser (FDPAL), a significant first step in the direction of high-power laser systems exhibiting the necessary thermal management characteristics.

Early DPAL demonstrations relied on the use of gain media in static cell configurations, an approach that effectively limits the amount of heat deposited into a system before thermal effects begin to degrade performance. By incorporating flow technology into the standard DPAL design, the FDPAL innovation achieves the same effect: removing heat from the gain medium and thereby improving overall beam quality.

Several recent research papers in the SPIE Digital Library also report advances with alkali lasers, most recently with power scalability.

B.V. Zhdanov, M.K. Shaffer, and R.J. Knize of the USAF Academy in Colorado reported the results of a variety of experiments on alkali lasers at SPIE Photonics Europe in Brussels in June. They demonstrated efficient Rb, Cs and K vapor lasers and the high potential of these lasers as a scalable source of high-power laser radiation in the near-infrared range.

They also performed power scaling experiments with multiple diode-laser pumping sources and diode-pumped alkali vapor amplifiers.

“As a result of this effort, we have increased the alkali lasers output power to tens of watts in continuous wave operation,” the authors report in “Alkali lasers: a new type of scalable high-power laser.”

Source: Proceedings of SPIE 7721, 77211V (2010); doi:10.1117/12.853409.

Silicon boosts photon detectors

A team of researchers at Delft University of Technology (Netherlands), Heriot-Watt University (UK), and the National Institute of Standards and Technology (USA) have developed a telecom-wavelength, single-photon detector with niobium-titanium-nitride (NbTiN) superconducting nanowires on oxidized silicon.

Their superconducting nanowire single-photon detector (SNSPD) reached a peak practical detection efficiency of 23% at 1310 nm, highly promising for high-speed, low-noise photon counting at telecommunications wavelengths.

Full chip and fiber arrangement, below, showing substrate layer structure, not to scale. 

full chip and fiber arrangement, not to scale.Their research was reported at the Advanced Photon Counting Techniques conference at SPIE Defense, Security, and Sensing in April 2010 and in the June 2010 issue of Applied Physics Letters.

The detectors are a key enabling technology for a host of demanding infrared photon counting applications, from quantum cryptography to new methods of imaging and ranging. They offer picosecond timing jitter, short recovery times, and low dark counts even in free running mode. The detectors operate at approximately 4K, a temperature which can now be attained using compact and efficient closed-cycle refrigerators rather than liquid cryogens.

Their device is fabricated on an oxidized silicon substrate. The high refractive index difference between the oxide and silicon beneath gives a strong reflection, like a cat’s eye, according to SPIE member Robert Hadfield of Heriot-Watt University, a co-author of the Letters paper. Hadfield chaired a session on superconducting single-photon detectors and was an invited speaker at the conference in April.

By picking the right oxide thickness, the absorption at the superconducting detector can be maximized at the wavelength of choice, Hadfield says. The devices were fiber coupled and characterized at a range of wavelengths.

figure showing system detection efficiency

System detection efficiency (DE) with varying wavelength. The increased efficiency near to the design wavelength of 1310nm is due to increased photon absorption because of the cavity layer structure. The small fluctuations are caused by the additional cavity formed between the fiber end and the device surface. Figures courtesy Mike Tanner.

“Further improvements are within reach using high reflectivity silicon on insulator mirrors,” says TU Delft’s Val Zwiller, also a coauthor of the Letters article. “Superconducting nanowire devices on silicon substrates would also be compatible with other advanced photonic components such as photonic crystal cavities, plasmonic structures, and optical waveguide circuits.”

Source: Applied Physics Letters 96, 221109 (2010).

OLED, PV research in Journal of Photonics for Energy

The new SPIE Journal of Photonics for Energy (JPE) launches this January with papers covering OLEDs, photovoltaic technologies, and other applications of photonics for renewable and efficient energy.

SPIE Fellow Zakya Kafafi of the National Science Foundation (USA) is editor-in-chief of the new peer-reviewed electronic journal. It will be free to read in the SPIE Digital Library for the first year.

JPE covers fundamental and applied photonics research areas focused on energy harvesting, conversion, storage, distribution, monitoring, consumption, and efficient usage. Its first issue includes several papers based on OLED and PV research presented at two conferences at SPIE Optics and Photonics 2010.

“Recognizing the need for a cohesive source for publications focused on photonics for energy applications, SPIE is pleased to provide an innovative electronic journal that will share research results with the international community to help advance solutions to the world’s needs for energy production, storage, transmission, efficiency, and clean technology,” says SPIE President Ralph James.

Information about the journal, along with submission information for authors, is available at spie.org/jpe

Imaging: In life as in death

Scientists at University at Buffalo (USA) have combined several imaging techniques to provide new information about the life cycle as well as the death process of macromolecules.

In a study published in the October 2010 issue of Biophysical Journal, Artem Pliss, Andrey Kuzmin, Aliaksandr Kachynski, and Paras Prasad combined Raman microspectrometry, coherent anti-Stokes Raman scattering (CARS), and two-photon excited fluorescence (TPEF) nonlinear optical microscopy to visualize macromolecular organization of the nucleus throughout the mitotic cell cycle.

“The overall analysis of the Raman spectroscopy and CARS/TPEF imaging data in HeLa cells supports the view that the cell nucleus employs thermodynamic diffusion for transport of macromolecules,” they concluded.

Prasad will discuss the study of the dynamics in live cells 22 January at a Hot Topics session at BiOS, part of SPIE Photonics West in San Francisco.

See related story.

Metamaterial for ultrasound

American and Spanish scientists have found a way to improve the resolution of the pictures captured in ultrasound imaging.

In a paper in the journal Nature Physics in November, physicists at University of California, Berkeley, and Universidad Autonoma de Madrid demonstrate how to capture evanescent waves bouncing off an object to reconstruct detail as small as one-fiftieth of the wavelength of the sound waves.

“With our device, we can pick up and transmit the evanescent waves, which contain a substantial fraction of the ultra-subwavelength information from the object, so that we can realize super-resolution acoustic imaging,” says first author Jie Zhu, a post-doctoral fellow at UC Berkeley.

The device is a three-dimensional, holey-structured metamaterial consisting of 1600 hollow copper tubes bundled into a 16-centimeter bar with a square cross-section of 6.3 cm. Placed close to an object, the structure captures the evanescent waves and pipes them through to the opposite end.

In a practical device, Zhu says, the metamaterial could be mounted on the end of an ultrasound probe to vastly improve the image resolution. The device would also improve underwater sonography as well as nondestructive evaluation in industry applications.

“For ultrasound detection, the image resolution is generally in the millimeter range,” says co-author Xiaobo Yin. “With this device, resolution is only limited by the size of the holes.”

The work was performed in the laboratory of Xiang Zhang at Berkeley and based on theoretical predictions of the group led by Francisco J. García-Vidal of the Universidad Autonoma de Madrid. Other co-authors are J. Christensen of the Universidad Autonoma de Madrid, L. Martin-Moreno of CSIC-Universidad de Zaragoza in Spain, J. Jung from the Aalborg University in Denmark, and L. Fok of Berkeley.

Flexible display wins gold award

Photonics technologies won the top two prizes and several others in the Wall Street Journal’s 2010 Technology Innovation Awards.

flexible display
A flexible display from ITRI. Photo courtesy ITRI

Taiwan’s Industrial Technology Research Institute won the overall Gold Award for developing its a flexible universal panel for displays, FlexUPD, and Zoom Focus Eyewear took a silver award for TruFocal eyeglasses, which have a manual focus adjustment.

The key to ITRI’s technology that will allow mass production of FlexUPD is an ultra-thin and transparent soft plastic substrate and a non-stick de-bonding layer material that smoothly removes the substrate from the glass layer without damaging the electronics.

Researchers see the displays becoming e-books and e-maps, roll-up mobile phone screens, and medical sensors that could be wrapped around the body.

Others recognized in 17 categories were:

• Lightfleet Corp.: method of using beamed light instead of copper or fiber-optic wires in connecting computer processors

• NanoLumens, flexible digital displays

• Solexant Corp.: ultrathin-film inorganic solar PV cells

• Life Image Inc: cloud-based platform for sharing and storing diagnostic images

• Aribex: hand-held dental x-ray device

• BriefCam: browsing technology for viewing surveillance video

• Liquid Robotics: unmanned seagoing craft with instruments powered by a solar panel

• InVisage Technologies: image sensor for digital cameras that uses semiconducting nanocrystals for light capture.

• STMicroelectronics: smart multisensory devices to measure movement, pressure, temperature and altitude

• Nanosys: semiconductor component for notebooks and mobile devices.

QCL lasers subject of special journal section

Advances in quantum cascade laser (QCL) technology and its many applications are the subject of a special section in the November issue of the SPIE journal Optical Engineering.

QCL technology enables compact, powerful, and efficient infrared (IR) sources that meet industrial and military needs and highly sensitive, low-cost, field-friendly, narrow-line lasers for spectroscopic applications such as atmospheric monitoring.

photo of Federico CapassoAuthors in the special section include SPIE Fellows Federico Capasso of Harvard University and leader of the group who first demonstrated QCL technology 16 years ago at Bell Labs; Kumar Patel, developer of the first CO2 laser and CEO of Pranalytica; Manijeh Razeghi of Northwestern University; and other leading international researchers.

Capasso, who was awarded the Berthold Leibinger Future Prize and the Julius Springer Prize for Applied Physics earlier this year, contributed an invited review paper to the 26-article special section. The article, "High-performance midinfrared quantum cascade lasers," is freely available to all as an introduction to both the QCL field and the special section on QC lasers.

The article can also be accessed via SPIE Reviews, an open-access journal that includes original review articles as well as selected review articles from all SPIE journals.

U.S. Naval Research Laboratory scientists Jerry Meyer and Igor Vurgaftman are the special section editors.

Sharma editor of Journal of Electronic Imaging

Gaurav SharmaSPIE member Gaurav Sharma, associate professor at University of Rochester (USA) and former director of the Center for Emerging and Innovative Sciences in New York, is the new editor of the SPIE/IS&T Journal of Electronic Imaging (JEI). Sharma has served as an associate editor for the journal and is the editor of the Digital Color Imaging Handbook published by CRC Press in 2003.

An inventor on more than 40 U.S. patents, with several additional patents pending, Sharma succeeds Jan Allebach who served as JEI editor since 2001.

JEI is co-published by SPIE and the Society for Imaging Science and Technology (IS&T). It disseminates peer-reviewed papers online in article-at-a-time mode and quarterly in print.

SPIE biomedical optics journal to publish monthly

The SPIE Journal of Biomedical Optics is doubling its publication frequency with the transition from bimonthly to monthly in January.

The change enables the journal to continue the steady growth in size and impact it has seen since its launch in 1996 as a quarterly and to better manage the increasing number of submissions, says editor-in-chief Lihong Wang.

“The growth of the journal is in line with the growth of the field of biomedical optics,” Wang says, becoming “the default choice for the field.”

The journal has helped define the field of biomedical optics with special sections on high-impact topics, many of which have been ‘firsts’ for the scientific community.

More information.

Have a question or comment about this article? Write to us at spieprofessional@spie.org.

DOI: 10.1117/2.4201101.06

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