Wide-angle, broadband, and highly efficient holography

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Coupled dipole-patch nano-antenna cells are used in a new approach to impose an arbitrary phase profile on reflected light.
28 January 2016, SPIE Newsroom. DOI: 10.1117/2.1201512.006252

Computer-generated holography is a widely used technology for various applications, e.g., from authentication and optical data storage, to interferometry, particle trapping, and phase conjugation.1–4 In these applications, complex waveforms are radiated efficiently at small angles from the holographic elements. Alternatively, simple grating lobes—with specific resonant conditions—can be used to project the waveforms at larger angles.5–7 To achieve wide-angle projection of computer-generated holograms, a steep phase gradient between adjacent pixels is required. To attain such a gradient, however, a small number of pixels in each period is needed and the projected hologram is therefore inefficient.8–10 Efficient projection of complex waveforms at large angles thus remains a challenge.11, 12

An alternative approach for the generation of complex reflective patterns involves the use of nano-antenna-based metasurfaces. Nano-antennas, which are nanometer-sized metallic structures, resonate at optical frequencies and are essentially a scaled-down counterpart of conventional radio-frequency antennas.13–16 In some recent studies, the use of nano-antennas for holography has been demonstrated.17–21 These previous investigations, however, have mostly focused on optical transmission metasurfaces. This has limited the measured efficiency levels to below 10%.

In this work, we propose and demonstrate the use of a nano-antenna reflectarray for efficient, broadband, and wide-angle holography applications.22 We use our reflectarray, which is composed of optical nano-antenna elements in a coupled dipole-patch configuration, to control the phase of the scattered light. Before we are able to realize our nano-antenna-based hologram approach, we have to determine the phase map that corresponds to the desired output beam. We thus implement the Gerchberg-Saxton algorithm23, 24 for this purpose. We have chosen the logo of Tel Aviv University as the pattern for the demonstration of our technique. During the demonstration, we projected this logo at angles of 20 and 45°, relative to the incident beam. The required phase map and the corresponding optical output are shown in Figure 1, as well as an illustration of the holography concept.

Figure 1. Demonstration of the nano-antenna reflectarray holography approach.20The (a) phase map and (b) simulated far-field image of the Tel Aviv University logo are shown. AU: Arbitrary units. (c) Illustration of the experimental concept. θ: Angle of projection.

The next step in our approach is to design nano-antennas that scatter light with the desired phase. The antennas are chosen so that the continuous phase is quantized into six discrete values between 0 and 300° (in 60° increments). To span the phase completely, we find that it is advantageous to use unit cells that comprise two antenna elements with different geometries. The combined spectral response of the two elements provides more degrees of freedom for the design and facilitates 2π-phase spanning. We used the technique of electron-beam lithography to fabricate our nano-antenna arrays (see Figure 2).

Figure 2. Optical microscope (a) and scanning electron microscope (b) images of a fabricated nano-antenna array. (c) A high-magnification scanning electron microscope image of the region indicated.20The array consists of 256×256 unit cells, and each unit cell is a 720nm-side square. The final device therefore has dimensions of 184×184μm.

To achieve a high efficiency with our technique, the reflectivity of the individual elements should differ only in phase and a constant amplitude should be maintained. By properly selecting the dimensions of our antenna elements—see Figure 3(b)—it is possible to attain a scattered wave that possesses any required phase response, while retaining a uniform amplitude. By varying the dimensions of these elements, we can alter the combined antenna response, which in turn changes the phase of the reflected wave. We conduct the optimization of the nano-antennas over a supercell consisting of the six phase pixels, organized in sequence from 0 to 300°, as shown in Figure 3(a). We simulate the supercell in an infinite 2D array, which enables a computationally efficient optimization of the elements. It is also possible to modify the element dimensions in the supercell. We can thus optimize the phase response and obtain the final element dimensions.

Figure 3. Unit cell geometry of the supercell used for nano-antenna optimization.20(a) Top view of the unit cells. Au: Gold. Cr: Chromium. Si: Silicon. SiO2: Silica. L: Length. W: Width. (b) Phase response (top) and amplitude response (bottom) of the antenna elements. Stars in (b) indicate the dimensions of the dipole and patch nano-antennas, which are obtained during the supercell optimization.

The scattering efficiency of our resultant hologram is illustrated in Figure 4. These measurement results indicate that the efficiency remains high over a spectral range of 200nm. This broadband response is caused by the phase response of our designed nano-antennas, which is strongly wavelength independent. We also find that the image projected by the hologram remains unchanged. For comparison, the theoretical efficiencies of the phase-quantized hologram projected at 20 and 45° are 60 and 55%, respectively. Our measured efficiency is therefore only slightly lower than the theoretical predictions. This difference arises from fabrication errors and optimization tolerances.

Figure 4. Efficiency measurements for the 20°(dashed red) and 45° (solid blue) holograms. The inset is an image of the projected hologram.20λ: Wavelength.

We have demonstrated a new wide-angle, highly efficient optical holography approach in which we use a reflectarray of optical nano-antenna elements to control the phase of the scattered light. In our methodology, we use the Gerchberg-Saxton algorithm to determine the phase map that is required to project our chosen pattern at angles of 20 and 45°, relative to the surface normal. We found that the measured efficiency of the projected hologram is between 40 and 50% over a broad wavelength range. To further improve the efficiency of our holographic technique, we need to develop new methods to eliminate phase and fabrication errors. Moreover, by incorporating an active tuning mechanism, it may be possible to extend our approach and thus realize active holographic displays and communication devices.


Jacob Scheuer, Yuval Yifat, Michal Eitan-Wiener, Zeev Iluz, Yael Hanein, Amir Boag

 


References:
1. L. Dhar, K. Curtis, T. Fäcke, Holographic data storage: coming of age, Nat. Photon. 2, p. 403-405, 2008.
2. G. Pedrini, W. Osten, M. E. Gusev, High-speed digital holographic interferometry for vibration measurement, Appl. Opt. 45, p. 3456-3462, 2006.
3. J. Liesener, M. Reicherter, T. Haist, H. J. Tiziani, Multi-functional optical tweezers using computer-generated holograms, Opt. Comm. 185, p. 77-82, 2000.
4. G. W. Burr, I. Leyva, Multiplexed phase-conjugate holographic data storage with a buffer hologram, Opt. Lett. 25, p. 499-501, 2000.
5. M. Oliva, T. Harzendorf, D. Michaelis, U. D. Zeitner, A. Tünnermann, Multilevel blazed gratings in resonance domain: an alternative to the classical fabrication approach, Opt. Express 19, p. 14735-14745, 2011.
6. M. A. Golub, A. A. Friesem, Effective grating theory for resonance domain surface-relief diffraction gratings, J. Opt. Soc. Am. A 22, p. 1115-1125, 2005.
7. H. Kogelnik, Coupled wave theory for thick hologram gratings, Bell Syst. Tech. J. 48, p. 2909-2947, 1969.
8. C. Pruss, S. Reichelt, V. P. Korolkov, W. Osten, H. J. Tiziani, Performance improvement of CGHs for optical testing, Proc. SPIE 5144, p. 460, 2003. doi:10.1117/12.500415
9. H. Zhou, F. Zhao, F. T. S. Yu, Angle-dependent diffraction efficiency in a thick photorefractive hologram, Appl. Opt. 34, p. 1303-1309, 1995.
10. C. Pruss, S. Reichelt, H. J. Tiziani, W. Osten, Computer-generated holograms in interferometric testing, Opt. Eng. 43, p. 2534-2540, 2004. doi:10.1117/1.1804544
11. O. Barlev, M. A. Golub, A. A. Friesem, M. Nathan, Design and experimental investigation of highly efficient resonance-domain diffraction gratings in the visible spectral region, Appl. Opt. 51, p. 8074-8080, 2012.
12. D. C. Oshea, T. J. Suleski, A. D. Kathman, D. W. Prather, Diffractive Optics: Design, Fabrication, and Test, p. 260, SPIE Press Book, 2003.
13. P. Bharadwaj, B. Deutsch, L. Novotny, Optical antennas, Adv. Opt. Photon. 1, p. 438-483, 2009.
14. L. Novotny, N. van Hulst, Antennas for light, Nat. Photon. 5, p. 83-90, 2011.
15. S. Bozhevolnyi, T. S⊘ndergaard, General properties of slow-plasmon resonant nanostructures: nano-antennas and resonators, Opt. Express 15, p. 10869-10877, 2007.
16. N. Berkovitch, P. Ginzburg, M. Orenstein, Nano-plasmonic antennas in the near infrared regime, J. Phys.: Cond. Matter 24, p. 073202-073217, 2012.
17. Y. Montelongo, J. O. Tenorio-Pearl, W. I. Milne, T. D. Wilkinson, Polarization switchable diffraction based on subwavelength plasmonic nanoantennas, Nano Lett. 14, p. 294-298, 2014.
18. S. Larouche, Y.-J. Tsai, T. Tyler, N. M. Jokerst, D. R. Smith, Infrared metamaterial phase holograms, Nat. Mater. 11, p. 450-454, 2012.
19. X. Ni, A. V. Kildishev, V. M. Shalaev, Metasurface holograms for visible light, Nat. Commun. 4, p. 2807, 2013. doi:10.1038/ncomms3807
20. Y. Yifat, M. Eitan, Z. Iluz, Y. Hanein, A. Boag, J. Scheuer, Highly efficient and broadband wide-angle holography using patch-dipole nanoantenna reflectarrays, Nano Lett. 14, p. 2485-2490, 2014.
21. J. Scheuer, Y. Yifat, Holography: metasurfaces make it practical, Nat. Nanotech. 10, p. 296-298, 2015.
22. J. Scheuer, Y. Yifat, M. Eitan-Wiener, Z. Iluz, Y. Hanein, A. Boag, Plasmonic holography: obtaining wide angle, broadband, and high efficiency, Proc. SPIE 9547, p. 95470L, 2015.doi:10.1117/12.2190701
23. R. W. Gerchberg, W. O. Saxton, A practical algorithm for the determination of phase from image and diffraction plane pictures, Optik 35, p. 237-246, 1972.
24. J. R. Fienup, Phase retrieval algorithms: a comparison, Appl. Opt. 21, p. 2758-2769, 1982.
Source:
http://spie.org/newsroom/technical-articles/6252-wide-angle-broadband-and-highly-efficient-holography?highlight=x2422&WT.mc_id=KNROPTOENGE

Plasmonic optical tweezers: A long arm and a tight grip

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nature

By taking advantage of the thermal gradient that is generated in plasmonic systems and by using an a.c. field, plasmonic tweezers can have a large radius of action and can trap and manipulate single nano-objects.

 

To have access to this paper, please visit:

http://www.nature.com/nnano/journal/v11/n1/full/nnano.2015.253.html

Plasmons Enhance Detection of Wavefront Aberrations

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DUBLIN, Dec. 8, 2015 — A sensor that exploits plasmonics to gauge nanoscale distortions in lightwaves could yield more powerful tools for metrology and chemical sensing, as well as sharper microscopes.

The method detects wavefront aberrations indirectly by measuring changes in the reflectivity of gold films. It may be the first to use plasmons to address a classical optics problem, according to its developers at University College Dublin.

As light travels through water, the atmosphere and even human tissue its wavefront becomes distorted, blurring images and reducing resolution. It’s possible to correct for these distortions with adaptive optics by precisely measuring the shape of the wavefront.

Such measurements — albeit on relatively large scales — are used in astronomy to correct for atmospheric distortion.

Conventional wavefront sensors work by either mechanically sampling wavefronts with microlenses or other devices or measuring interference patterns. The latter approach requires the extra step of ensuring that the interacting light waves are in phase — meaning their waveforms overlap precisely.

distortions


Cartesian wavefront derivatives can be determined by monitoring intensity variations across the reflected beam of light used to excite surface plasmon polaritons in the Kretschmann configuration. Courtesy of Optica/The Optical Society.


Now, by observing how efficiently incoming light creates surface plasmon polaritons (SPPs) on gold film, it’s possible to derive previously undetectable nanoscale distortions in the wavefronts.

SPPs arise when light meets an electrically conducting material, causing electrons to oscillate in a wavelike pulse that travels across the material’s surface. Any changes in the angle of incidence — as would occur from a distortion in the wavefront — affects the way the SPPs are formed. This directly affects how much light is reflected back from the surface.

“Since these polaritons are perfectly coupled to the light that forms them, any changes in their behavior would indicate a change in the waveform of light,” said Brian Vohnsen, a senior lecturer at University College Dublin. “We make use of the attenuation of the signal from the gold surface to simply convert the wavefront shape — or slope — into an intensity difference in a beam of light.”

This change is captured with cameras that are sensitive to minute changes in intensity.

To fully reconstruct the wavefront, the system requires two separate measurements made at 90° to one another. It is then possible to calculate the tiny changes in the actual wavefront based on the orthogonal intensity data points. The speed of the measurement is limited only by the speed of the cameras.

This type of sensor may find applications in the quality inspection of planar materials, films and coatings, the researchers said. It could also replace some wavefront sensors used in astronomy, microscopy and vision science.

The researchers are working to overcome two limitations in the current setup. The first is the requirement for simultaneous measurement of wavefront changes with two cameras. The second is improving the method by which the SPPs are “excited” on the surface of the gold film.

The results were published in Optica (doi: 10.1364/optica.2.001024 [open access]).

 

Reference: http://www.photonics.com/Article.aspx?PID=6&VID=124&IID=855&AID=58043

SPIE Optics + Photonics

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spieeeeee

 

SPIE Optics + Photonics 2016, the largest international, multidisciplinary optical sciences and technology meeting in North America. The meeting where the latest research in optical engineering and applications, sustainable energy, nanotechnology, and organic photonics is presented.

 

For more information, please visit the following website:

http://spie.org/conferences-and-exhibitions/optics-and-photonics

CLEO: 2016

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cleo

The leading peer-reviewed meeting on lasers & electro-optics.

CLEO (Conference on Lasers and Electro-Optics) serves as the premier international forum for scientific and technical optics, uniting the fields of lasers and opto-electronics by bringing together all aspects of laser technology, from basic research to industry applications.

Attendees have the opportunity to hear and present groundbreaking research, share ideas, and network with colleagues and luminaries. CLEO presents a world-renowned peer-reviewed program and offers high quality content from five core event elements:

ICNP 2016 The 9th International Conference on Nanophotonics

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The International Conference on Nanophotonics (ICNP) will be held from 21-25 March 2016 at Academia Sinica, Taipei, Taiwan.

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This conference is a unique event where the latest advances in optics and photonics both in nano- and micro-scale will be reported and discussed. This conference primarily aims to explore novel ideas in nanophotonic science and technology that might enable technological breakthroughs in high impact areas such as biomedical and life sciences; information processing; communications; energy harvesting and storage; environment and conservation. The comprehensive coverage of conference themes, including microscopy and nanoscopy, silicon photonics; quantum optics; metamaterials; plasmonics; transformation optics; materials for micro- and nano-photonics; nanofabrication; and photonic devices, ensures researchers in this exciting field always have the opportunity to report their work and exchange information with fellow co-workers.

ICONN 2016 – International Conference on Nanoscience and Nanotechnology 7-11 Feb 2016

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ICONN

National Convention Centre, Canberra, Australia

The aim of the 2016 International Conference On Nanoscience and Nanotechnology (ICONN 2016) is to bring together Australian and International communities (students, scientists, engineers and stake holders from academia, government laboratories, industry and other organisations) working in the field of nanoscale science and technology to discuss new and exciting advances in the field. ICONN will cover nanostructure growth, synthesis, fabrication, characterization, device design, theory, modeling, testing, applications, commercialisation, and health and safety aspects of nanotechnology.

The conference will feature plenary talks followed by technical symposia (parallel sessions) consisting of invited talks, oral and poster presentations.

Infrared spectroscopy with visible light

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Experimental set-up. A continuous-wave laser at 532 nm pumps two nonlinear crystals, where SPDC occurs. The crystals are placed in a vacuum chamber and CO2 is injected into the chamber. The interference pattern of the SPDC from the two crystals is imaged by a lens onto a slit of a spectrograph and recorded by a charge-coupled device (CCD) camera.

Spectral measurements in the infrared optical range provide unique fingerprints of materials, which are useful for material analysis, environmental sensing and health diagnostics1. Current infrared spectroscopy techniques require the use of optical equipment suited for operation in the infrared range, components of which face challenges of inferior performance and high cost. Here, Kalashnikov et al. develop a technique that allows spectral measurements in the infrared range using visible-spectral-range components. The technique is based on nonlinear interference of infrared and visible photons, produced via spontaneous parametric down conversion. The intensity interference pattern for a visible photon depends on the phase of an infrared photon travelling through a medium. This allows the absorption coefficient and refractive index of the medium in the infrared range to be determined from the measurements of visible photons. The technique can substitute and/or complement conventional infrared spectroscopy and refractometry techniques, as it uses well-developed components for the visible range

Reference:

Nature Photonics 10, 98–101 (2016) doi:10.1038/nphoton.2015.252
http://www.nature.com/nphoton/journal/v10/n2/full/nphoton.2015.252.html

Plasmonic Device Achieves 90-GHz Switching

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DURHAM, N.C., July 27, 2015 — Able to flip on and off 90 billion times a second, a new plasmonic light emitter could form the basis of optical computing.

“This is something that the scientific community has wanted to do for a long time,” said Duke University professor Maiken Mikkelsen, whose team developed the device. “We can now start to think about making fast-switching devices based on this research, so there’s a lot of excitement about this demonstration.”

The device consists of a 75-nm silver cube and a thin sheet of gold, with 6-nm quantum dots (QDs) sandwiched in between. Laser illumination generates plasmons on the cube’s surface, which creates an intense electromagnetic field that triggers the QDs, producing directional, efficient emission of photons that can be turned on and off at a rate of more than 90 GHz.

Superfast fluorescence system


Transmission electron microscope view of a superfast fluorescence system. The silver cube is 75 nm wide. The quantum dots (red) are sandwiched between the silver cube and a thin gold foil. Courtesy of Maiken Mikkelsen/Duke University.


“There is great interest in replacing lasers with LEDs for short-distance optical communication, but these ideas have always been limited by the slow emission rate of fluorescent materials, lack of efficiency and inability to direct the photons,” said postdoctoral researcher Gleb Akselrod. “Now we have made an important step towards solving these problems.”

“The eventual goal is to integrate our technology into a device that can be excited either optically or electrically,” said Thang Hoang, also a postdoctoral researcher in Mikkelsen’s laboratory. “That’s something that I think everyone, including funding agencies, is pushing pretty hard for.”

The group is now working to use the plasmonic structure to create a single-photon source — a necessity for extremely secure quantum communications — by sandwiching a single QD in the gap between the silver nanocube and gold foil. They are also trying to precisely place and orient the QDs to create the fastest fluorescence rates possible.

Aside from its potential technological impacts, the research demonstrates that well-known materials need not be limited by their intrinsic properties, the researchers said.

“By tailoring the environment around a material, like we’ve done here with semiconductors, we can create new designer materials with almost any optical properties we desire,” Mikkelsen said. “And that’s an emerging area that’s fascinating to think about.”

Funding came from the U.S. Air Force Office of Scientific Research, an Oak Ridge Associated University’s Ralph E. Powe Junior Faculty Enhancement Award, the Lord Foundation of North Carolina and the Intelligence Community Postdoctoral Research Fellowship Program.

The research was published in Nature Communications (doi: 10.1038/ncomms8788).

For more information, visit www.duke.edu.

 

Source: http://www.photonics.com/Article.aspx?PID=6&VID=124&IID=830&AID=57603

 

Plasmon Wakes Created, Controlled in Metamaterial

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CAMBRIDGE, Mass., July 7, 2015 — Surface plasmons can exhibit wakes likes any other wave, and those wakes can be controlled through nanoscale features on a metallic surface and through properties of the light shining on it.

The creation and control of surface plasmon wakes could lead to new types of plasmonic couplers and lenses that could create 2D holograms or focus light at the nanoscale, according to researchers at Harvard University.

“The ability to control light is a powerful one,” said professor Federico Capasso. “Our understanding of optics on the macroscale has led to holograms, Google Glass and LEDs, just to name a few technologies. Nano-optics is a major part of the future of nanotechnology, and this research furthers our ability to control and harness the power of light on the nanoscale.”

Plasmon wake


An artist’s rendering of a running wave of polarization that excites the surface plasmon wakes. Courtesy of Daniel Wintz, Patrice Genevet and Antonio Ambrosio.


Capasso’s team generated running waves of polarization that propagated faster than the phase velocity of the plasmons along a 1D metamaterial. This created wakes analogous to those responsible for Cherenkov radiation.

The metamaterial, a nanostructure of rotated slits etched into a gold film, changes the phase of the surface plasmons generated at each slit relative to each other, increasing the velocity of the running wave. The nanostructure also acts like a boat’s rudder, allowing the wakes to be steered by controlling the speed of the running wave.

The angle of incidence and photon spin angular momentum of the light shining onto the metamaterial determines the speed of the running wave of polarization and thus provides an additional measure of control. The team also discovered that using polarized light can even reverse the direction of the wake relative to the running wave — like a wake traveling in the opposite direction of a boat.

“Being able to control and manipulate light at scales much smaller than the wavelength of the light is very difficult,” said graduate student Daniel Wintz. “It’s important that we not only observed these wakes but found multiple ways to control and steer them.”

The observation itself was challenging, as “surface plasmons are not visible to the eye or cameras,” said Antonio Ambrosio, a postdoctoral fellow at Harvard and researcher at the Italian Research Council. “In order to view the wakes, we used an experimental technique that forces plasmons from the surface, collects them via fiber optics and records the image.”

This work could represent a new testbed for wake physics across a variety of disciplines, the researchers said.

“This research addresses a particularly elegant and innovative problem in physics which connects different physical phenomena, from water wakes to sonic booms, and Cherenkov radiation,” said Patrice Genevet, a former Harvard postdoctoral scholar currently affiliated with the Singapore Institute of Manufacturing Technology.

Funding came from the National Science Foundation and U.S. Air Force Office of Scientific Research.

The research was published in Nature Nanotechnology (doi: 10.1038/nnano.2015.137).

For more information, visit seas.harvard.edu.

 

Source: http://www.photonics.com/Article.aspx?PID=5&VID=125&IID=838&AID=57563