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Mar 26

Taking a look around an airport, bus station, or waiting room, you’re likely to notice a few differences between the scenes now as compared to those of ten or so years ago. One thing that might strike you is that the papery time killers that filled lounging areas from the past are now replaced with personal electronic devices. Thanks to a great number of innovations, including the sophistication of LCDs, LEDs, electronic ink, and microprocessors, portable devices for reading purposes and beyond are becoming ubiquitous.

However, you might notice another striking difference between then and now with respect to these typeface transporters. It’s probably a tiny daily burden you’ve learned to cope with over the years: you can’t exactly roll up your electronic device like your morning newspaper. And I wouldn’t recommend trying it, but go for it if you don’t believe me (disclaimer: I’m not buying you a new phone, tablet, e-reader, or whatever you just broke).

Luckily, there are always smart folks who see these issues, as well as a handful of others: Why can’t I wear my electronics and photonics on my skin? Why can’t I cram my devices into any arbitrary space I want? Why should I have to look at these things but not through them?

Thanks to many forward-thinking materials researchers, the answer to the above questions seems to be, “No reason, let’s make it happen!” So here we are in the age of developing flexible electronics and photonics. The difficulty in making devices flexible is probably pretty obvious: most materials we conventionally use are not flexible! However, that doesn’t mean we can’t make a materials change for some things. For example, polymers are very flexible, so any pieces we can make out of those types of materials could be very helpful. And it turns out for photonics, you can make emitters, modulators, filters, and waveguides out of such materials as well as other organic and inorganic materials.

Nevertheless, if you’re like me, you have a hard time parting with semiconductors. They’re just so good at what they do and doing it efficiently. Well, there’s not necessarily any reason to abandon our band-gap-having, crystalline friends. It’s just that they need to trim down a little, to relieve a bit of the strain. The amount the most stressed crystalline layer needs to stretch or compress upon a deformation is related to how many layers away it is from the neutral plane, where there is no strain. Translation: make the layer thin.

So now you can bend your semiconductor, and you have an efficient source flapping in the breeze. Unfortunately, if you left it just like this, it would fall apart in an instant, its thickness being measured in units of nanometers (hence, nanomembranes). That’s why techniques have been developed to put these membranes on more stable yet flexible substrates. Enter again polymers. Two methods dominate at this time: transfer printing and direct patterning. Transfer printing is a process in which devices are fabricated and then bonded to the flexible substrate. This allows one to put a multitude of different devices, possibly made of different materials, on a single substrate. On the other hand, direct patterning utilizes deposition of a material on the substrate and then etching steps to define the devices. Although often less versatile than transfer printing, direct patterning is another robust method of making this flexible hybrid platform.

General process illustration for crystalline semiconductor membrane release, transfer and stacking. (a) Begin with source material (e.g., SOI, GeOI, III-V multi layers with a sacrificial layer). Metallization can be applied here, if needed. (b) Pattern top layer into membrane (or strip forms) down to the sacrificial layer. (c) Release membrane by undercutting the sacrificial layer. (d) Fully released membrane settles down on the handling substrate via van der Waals force (“in-place bonding”). Direct flip transfer: (e1). Apply glue on host (e.g., flexible) substrate and attach it to the handling substrate. (f1) Lift-up the host substrate and flip to complete the transfer. Glue can be dissolved if needed. Stamp-assisted transfer: (e2) Bring a stamp (e.g., Polydimethylsiloxane, or PDMS) toward the handling substrate, press and lift-up. (f2) Apply the stamp with membrane attached to a new host substrate (which can be coated with glue, but not necessary). (g2) Slowly peel off the stamp or remove the stamp with shear force, leaving the membrane to stay on the new host substrate. Multiple layers can be applied by repeating (a)-(f1) or (a)-(g2). (Juejun Hu, Lan Li, Hongtao Lin, Ping Zhang, Weidong Zhou, and Zhenqiang Ma, "Flexible integrated photonics: where materials, mechanics and optics meet [Invited]," Opt. Mater. Express 3, 1313-1331 (2013))
 http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-3-9-1313)

General process illustration for crystalline semiconductor membrane release, transfer and stacking. (a) Begin with source material (e.g., SOI, GeOI, III-V multi layers with a sacrificial layer). Metallization can be applied here, if needed. (b) Pattern top layer into membrane (or strip forms) down to the sacrificial layer. (c) Release membrane by undercutting the sacrificial layer. (d) Fully released membrane settles down on the handling substrate via van der Waals force (“in-place bonding”). Direct flip transfer: (e1). Apply glue on host (e.g., flexible) substrate and attach it to the handling substrate. (f1) Lift-up the host substrate and flip to complete the transfer. Glue can be dissolved if needed. Stamp-assisted transfer: (e2) Bring a stamp (e.g., Polydimethylsiloxane, or PDMS) toward the handling substrate, press and lift-up. (f2) Apply the stamp with membrane attached to a new host substrate (which can be coated with glue, but not necessary). (g2) Slowly peel off the stamp or remove the stamp with shear force, leaving the membrane to stay on the new host substrate. Multiple layers can be applied by repeating (a)-(f1) or (a)-(g2). (Juejun Hu, Lan Li, Hongtao Lin, Ping Zhang, Weidong Zhou, and Zhenqiang Ma, “Flexible integrated photonics: where materials, mechanics and optics meet [Invited],” Opt. Mater. Express 3, 1313-1331 (2013))
 http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-3-9-1313)

With these methods, one can make a number of photonic (and electronic devices). And there are some interesting avenues for exploration. For example, despite the strain-mitigation provided by thinning semiconductor membranes, it does not provide strain-elimination. The presence of strain alters the electronic and photonic properties of semiconductors, and therefore one can make tunable devices through flexing the material. However, this isn’t always a good thing; it creates a tough problem to solve when you want an extremely stable device under bending stress.

As hopefully you can see, this is a very exciting and active area of research. There are many open research questions and progress is continuing. If this topic catches your interest and you’re attending CLEO 2014, a great opportunity to learn more is from an expert! John Rogers from the University of Illinois at Urbana-Champaign will be giving a tutorial on flexible photonic devices. So be sure to check it out!

 

Disclaimer: Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the United States Government and MIT Lincoln Laboratory.

Mar 21

Applications & Technology (A&T) is a key conference at CLEO: 2014, exploring the evolution of newly discovered technologies previously reported in CLEO: Science & Innovations as they are perfected and further developed to meet system and application requirements. New components, optoelectronics, and laser systems are demonstrated in real-world environments where innovative commercial technologies emerge.

Yu Chen, University of Maryland, Program Co- Chair provides an overview of this year’s A&T symposium and paper highlights.

CLEO Team:

Discuss the exciting lineup of symposia that are A&T related? What are some of the hot topics being covered?

Yu Chen:

This year we have organized a series of exciting symposia. The first two are focused on biomedical applications. The first one is Advances in Neurophotonics, organized by Drs. Nick Iftimia and Jin Kang. This symposium highlights the photonics technologies that enable mapping of brain function.  This is an important research area as highlighted by President Obama’s recent BRAIN Initiative. We have invited leaders in this field to share their frontier research. Topicscovered include optical coherence tomography and multi-photon microscopy for neuroimaging, high-resolution imaging of brain networks and diseases, and optogenetics.

Patient undergoing MEG. Wikipedia Commons

Patient undergoing MEG. Source: Wikipedia Commons

The second area of application is Molecular Imaging, which is an interdisciplinary area intersecting photonics technology and molecular medicine, with great potentials for early disease detection and personalized treatment. This year’s symposium, organized by Drs. Xavier Intes and Ali Azhdarinia, contains two sessions: one focuses on novel optical molecular imaging techniques, including near-infrared fluorescence imaging, Cerenkov radiation imaging, and photoacoustic imaging. The other session focuses on molecular probe development and clinical translation. The speakers are renowned scientists, clinicians, and industrial leaders that set the trend in this field.

The next two symposia are more technology oriented. The first one is Novel Light Sources and Photonic Devices in Optical Imaging, organized by Drs. Charles Lin, Nick Iftimia, and Ben Vakoc. This symposium highlights the advanced development of novel light sources and photonic technologies that enable biomedical imaging. Topics include novel light sources for nanophotonics-based OCT, as well as deep tissue multiphoton imaging and manipulation.

The next symposium has similar theme, but more focuses on Ultrashort Pulse Laser TechnologiesOrganizedby Drs. Ilko Ilev and Emma Springate, this symposium highlights the recent state-of-the-art development in ultrafast laser technologies for biophotonics and nanobiophotonics. Topics include ultrafast compact fiber lasers; tunable ultrafast visible, near- and mid-IR lasers; plasmonic nanobuble based integrated theranostics, and ultrafast laser induced ion beams for proton therapy.  

The next hot topic is Optofluidic Microsystems, organized by Drs. Ian White and Andreas Vasdekis. This symposium aims to highlight emerging trends in optofluidics and their application in microsystems.  This year’s program will feature an overview of the last ten years of optofluidics by one of the founding fathers of the field, Dr. Dmitri Psaltis, and will also project into the future by talks from current leaders in the field. Topics include optofluidic lasers and resonators, optofluidics for energy, and optofluidic particle manipulations.

CLEO Team:

What exciting papers did you receive for Applications & Technology?

Yu Chen:

We have a large affluence of papers for the light sources, resulting from the success of last year’s symposium on novel light sources. We also have papers focused on Neurophotonics, as stimulated by this year’s symposium. Our program includes new developments in OCT, multiphoton microscopy, and photoacoustic imaging, as well as clinical translation. Some of the example hot topics include adaptive optics for ophthalmology, point of care devices based on smart phones, minimally-invasive imaging technologies for disease diagnosis and therapy guidance, endomicroscopy, as well as multi-modal imaging combining OCT with fluorescence/confocal.

CLEO Team: Thank you


The CLEO Conference, sponsored by APS/Division of Laser Science, IEEE Photonics Society and the Optical Society received record-breaking submissions this year. The Conference takes place in San Jose, CA, USA, 8-13 June 2014.

For more information on CLEO: 2014 and the A&T program please visit www.cleoconference.org.

 

Mar 10

by David Norris,  Guest post

This is part 2 of a 3 part series post on the Controlled Light Propagation Incubator meeting at OSA headquarters in Washington, DC

Is it possible to look inside an object using only light reflected off the front?  Can you transmit more light through an attenuating medium by making it even thicker?  Could a bank verify your identity using the pattern of light scattered off your teeth?CT Scan image of brain

These tantalizing scenarios were among many presented during today’s meeting.  Though the focus remains on developing non-invasive deep imaging techniques for biological tissue, in particular using cameras and modulators placed only on the front side of a sample, the discussion also addressed more general questions on the theoretical limits of beam control and applications of scattering media to wide-field sensing.

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Re-posted from The Optical Society Blog

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Mar 07

by David Norris,  Guest post

This is part 3 of a 3 series post on the Controlled Light Propagation Incubator meeting at OSA headquarters in Washington, DC

After a final session of talks on new developments in 3D imaging methods and funding opportunities, our host Jerome Mertz presented a timely summary of outstanding problems and possible solutions identified during this week’s IncubatorPropagationmeeting meeting:

  • The main challenge remains increasing the signal from a point of interest in the face of a large background of diffuse light. Tools such as spatial light modulators can impart a signal gain up to the number of pixels, but no further.  Multi-photon techniques hold promise but require compensation of both spectral and spatial degrees of freedom.
  • The utility of the so-called “memory effect” for scanning a focus across a sample was much discussed, but without clear consensus on whether it can work in the completely diffusive regime.  An alternative is sampling at multiple separated spots, either sequentially or in parallel.

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Re-posted from The Optical Society Blog

Mar 07

by David Norris,  Guest post

This is part 1 of a 3 part series on the Controlled Light Propagation Incubator meeting at OSA headquarters in Washington, DC

example of biomedical imaging

Example of Biomedical imaging -source: wikipedia commons

The application of adaptive optics techniques–namely, optical wavefront shaping and phase modulation–to correct aberrations arising from highly scattering and disordered media holds tremendous promise for in vivo fluorescence imaging of biological tissue, and in particular the functional imaging of neural circuits. This topic has experienced an explosion of research activity in recent years, driven in large part by funding and interest from the BRAIN initiative, the Presidential focus aimed at mapping and unlocking the inner workings of the human brain. Following previous Incubator meetings in Optogenetics and Adaptive Optics, the organizers see today’s meeting as a natural next step.

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Re-posted from The Optical Society Blog

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