Advancing Photonic Functionalities

Advancing photonic functionalities

Professors Paul Steinhardt, Salvatore Torquato and Marian Florescu discuss hyperuniform p r ofesso r s materials use in the development of hyperuniform disordered solids, garnering better theoretical understanding of the physical properties of non-crystalline materials steinha r dt photonic integrated successfully recovered additional samples and circuits and other discovered other new mineral phases. applications without sensitive alignment of ST: Dr Frank Stillinger and I introduced the

material, waveguides concept of Hyperuniform Matter, characterised , to rq uato or cavities, and are by unusual suppression of density fluctuations, much less sensitive in 2003. Specifically, hyperuniform point to fabrication defects (particle) configurations are categorised – they contradict by vanishing infinite-wavelength density conventional wisdom fluctuations and encompass all crystals, and that PBG requires quasicrystals and special disordered many- To begin, could you outline your role within periodicity and anisotropy. Enabling freeform particle systems. This provides a means to flo r escu this project? circuit design and a reduction in defects makes place an umbrella over both crystalline and them the optimal material for virtually any special non-crystalline materials. HUDS PS: I am a theoretical physicist in the photonic application. These discoveries have can loosely be regarded as a state that is Department of Physics and Department been enabled by the invention of a universal intermediate between perfect crystals and of Astrophysics, Princeton University, and protocol for mapping point patterns into perfectly disordered materials. In 2008, we Director of the Princeton Center for Theoretical optimal designs. showed that stealthy HUDS can be created as Science. One of my longstanding interests is in disordered ground states and possess novel the structure and properties of non-crystalline We showed that it’s possible to introduce single-scattering properties, suggesting they states of matter because their properties are waveguides in HUDS that can have arbitrary may find applications in photonics. still poorly understood and, hence, have the shape and trap light in cavities with select potential for exhibiting surprising features. electromagnetic patterns. After discovering MF: I have been involved in the early studies these novelties, both theoretically and of quantum optical effects in photonic band ST: I am a theoretician in the Department numerically, we joined with experimental gap materials, while working in the group of of Chemistry, Department of Physics, and Professors Weining Man and Paul Chaikin to Professor Sajeev John, one of the inventors Princeton Institute for the Science and synthesise and test HUDS on the microwave- of the photonic crystal concept. My work on Technology of Materials. My scientific research and infrared-scale. quantum optical effects in photonic crystals covers statistical mechanics, condensed revealed coherent all-optical switching and matter, photonics and cancer modelling. Can you provide some insight into your transistor action in PGB materials. Subsequently, Amorphous states of matter have always research area? I developed the first general formalism for intrigued me; especially a new class called thermal emission in microstructured photonic hyperuniform materials (HM). PS: In 1984, Professor Dov Levine and I systems, which provides a comprehensive introduced the concept of quasicrystals, understanding of Planck’s radiation law MF: I am physicist in the Department of hypothetical solids with long-range modifications in these systems, rigorous design Physics and the Advanced Technology Institute, quasiperiodic translational order and principles for spectral and angular-selective University of Surrey. My research interests lie rotational symmetries that are forbidden absorbers and highly efficient solar cell and in the fields of nanophotonics, quantum optics, for periodic solids. Independently, Professor thermophotovoltaic components. and nanoelectronics. In particular, I focus Dan Shechtman and his collaborators found on the identification of novel phenomena aluminium and manganese alloys that we Do you have plans to extend R&D? and functionalities in artificially structured identified as matching the predicted diffraction photonic materials and in implementations of pattern for an icosahedral quasicrystal. In PS, ST & MF: We have partnered with linear-optical quantum information processing 2011, Shechtman won the Nobel Prize in industry to create a start-up company, in nanostructured materials. Chemistry for his experimental discovery. I Etaphase Inc, that will develop our scientific have since worked with various scientists to discoveries into a range of products, including What novel properties have you unearthed explore mathematical and elastic properties novel photonic integrated circuits for use in about photonic band gaps (PBG)? How will of quasicrystals. In 1998, I launched a computer datacenters, sensors, improved they have transferrable application? systematic search for natural quasicrystals that photovoltaics and displays. With an eye to culminated in the discovery 11 years later of potential end uses, we hope to continue both PS, ST & MF: Motivated by work on quasicrystalline grains in a CV3 carbonaceous basic science and applicationww and develop disordered HM, we discovered a new class of chondrite that formed 4.5 bn years ago, better theoretical understanding of PBG and photonic materials, known as hyperuniform making quasicrystals one of the first solids to other physical properties of HUDS. The path disordered solids (HUDS). Disordered and form in our solar system. I subsequently led a is full of challenges, but we do not foresee any isotropic – meaning they can be used in geological expedition to Kamchatka, where we showstoppers at this point.

www.researchmedia.eu 139 professors steinhardt, torquato and florescu Unlocking the potential of HUDS Physicists at Princeton University use novel computational tools and employ proven fabricating methods to discover the broader electronic and photonic applications of a new class of materials

Photonic bandgap (PBG) materials are The group has been developing two classes In an effort to find the optimal design of these synthetically designed materials that block light of novel non-crystalline designer materials, quasicrystals, Steinhardt joined with theorists for a finite band of energies and then transmit composed of photonic quasicrystals and Professor Salvatore Torquato, an expert on light with energies outside that band, similar hyperuniform disordered solids (HUDS), which hyperuniform materials and optimisation to the way in which a semiconductor acts for act as a photonic semiconductor. Principal problems, and photonics expert Florescu. Their electrons. The development of PBG materials is Investigator, Professor Paul Steinhardt, explains research led them to challenge the conventional seen as increasingly vital in the replacement of that their work has expanded the traditional view that periodicity or quasiperiodicity is electronics (electron transport) with photonics view of PBG materials by showing that HUDS, required to have a complete PBG. In doing so (light transport), which is necessary to realise whilst isotropic and with no translational order, they found that it is, in fact, possible to obtain the next generation of communications and have large and complete band gaps for both large complete band gaps in a new form of computer devices, as well as improved sensors, polarisations of light; a result which “contradicts material that is isotropic and disordered like LEDs, display devices and photovoltaics. the longstanding conventional wisdom that glass but also ‘hyperuniform’ like crystal. only crystalline materials have PBG”. He adds: The concept of hyperuniformity had been In order to control and manipulate light flow, “As photonic crystals are inherently anisotropic introduced and studied earlier by Torquato and specifically-designed defects can be introduced (blocking different bands of light propagating his colleague Dr Frank Stillinger. into PBG materials that make it possible to in different directions) they impose delicate transmit or trap specific frequencies within. constraints on designing photonic circuits, and “HUDS,” as Torquato expands, “have long-range Because these frequencies are far from those are also difficult to fabricate accurately”. density variations that are uniform like crystals, above and below the band gap, their behaviour even though they are isotropic”. They discovered is not degraded by mixing with modes with Because HUDS are isotropic and thus inherently that HUDS exhibit large, perfectly isotropic similar frequencies, thus enabling the ultimate disordered, they are less sensitive to fabrication band gaps, even though they are not periodic regulation of light flow. Through their invention defects and are an optimal base material which, or quasiperiodic. Since isotropy is enormously of a new form of PBG materials with unique co-PI Dr Marian Florescu (now based at Surrey advantageous in many optical applications, this symmetries and statistical properties, scientists University) suggests: “Have broad physical presented them with the opportunity to look at at Princeton University’s Department of Physics implications beyond photonic materials. It a new class of photonic solids with properties have delivered ground-breaking work with may become possible, for instance, to produce that are superior to photonic crystals and led numerous important applications. different types of hyperuniform structures and, to current experimentation on hyperuniform consequently, many distinct classes of novel disordered PBG materials. electronic or phononic systems”. Innovation in design Exploring electronic properties Initially a theoretical project, the work has now Steinhardt introduced, in 1984, along grown into a fully-fledged trial. Led by expert with his student Dov Levine, the concept theorists Steinhardt, Torquato and Florescu, of quasicrystals. These are solids with this collaborative effort into computer design quasiperiodic translational order and rotational and simulation of HUDS has been supported symmetry forbidden to crystals, such as fivefold by a National Science Foundation (NSF) symmetry in 2D and icosahedral symmetry in Early-concept Grant for Exploratory Research 3D. At that time, Steinhardt recognised that (EAGER). The research also benefits from the the question of being able to fully understand knowledge of Chaikin and Man who have been the electronic properties of quasicrystals fabricating and testing the theorists’ designs. had yet to be answered. In 2005, along with Professors Weining Man (San Fransisco State The objective is to explore the properties University) and Paul Chaikin (New York of these solids for novel isotropic photonic University), Steinhardt was presented with the devices, such as waveguides, splitters and opportunity to explore the band structure of wavelength-division multiplexers. There are a photonic quasicrystal that offered an easily some standard tools for fabricating photonic synthesised and precisely testable solid. “The crystals which are just as effective when photonic quasicrystal network,” he observed, applied to fabricating photonic quasicrystals “had a quasiperiodic pattern with icosahedral or HUDS. Methods include stereo-lithography, Figure 1. Electromagnetic Field Propagating through a rotational symmetry. Photonic quasicrystals, laser sintering, ‘toothpaste’ machines, direct hyperuniform disordered structure (semi-transparent we discovered, have a band gap that is more laser writing and e-beam lithography, all of region: dielectric hyperuniform structure, shades of blue/ isotropic than in photonic crystals – a highly which begin with a theoretical design that is red, maxima and minima of the electric field). desirable property for many applications.” then converted to a variation of computer-

140 International innovation Intelligence EAGER: Hyperuniform Disordered Photonic Band Gap Materials Objectives This research has important applications in optical To explore the properties of new photonic bandgap materials, called hyperuniform communications, energy harvesting, non-linear optics and disordered solids, for novel isotropic photonic improved light sources devices such as waveguides, cavities and splitters Key Collaborators aided design. Steinhardt points out that the possible in photonic crystals – and show that theoretical design is where innovation and optical cavities for trapping and manipulating Professor Paul Chaikin, New York University invention play a key role: “Depending on the light in a variety of modes can be designed Professor Weining Man, San Francisco State design, different energy bands are blocked in and densely arranged into the structure. The University different directions. HUDS are optimal in that collaborators have submitted two articles on they are isotropic and, hence, have isotropic HUDS that apply the ideas to novel waveguides Funding band gaps, giving them maximum flexibility and cavities and presented findings at a series National Science Foundation – award no. in photonic circuit design”. Florescu also of international conferences, including the 1041083 notes: “Benefiting from a unified approach 2012 American Physical Society meeting. for generating near-optimal photonic solids, Additionally, their research included a study Contact we are now ready to add an extra dimension that appeared in Applied Physics Letters in to our planar HUDS, opening the door for fully 2010 showing how band gap width and quality Professor Paul Steinhardt 3D-integrated optical devices”. degrade due to random fabrication defects. Principal Investigator This work has inspired the creation of a start- Department of Physics up company, Etaphase Inc, which aims to apply Broader impacts Princeton University research advances to photonic integrated realised from research Jadwin Hall, Room 214 & 404, circuits, sensors, photovoltaics and displays. Princeton, New Jersey 08544, USA The group is focused on developing fundamentally novel devices and NSF believes this work has the potential to T +1 609 258 1509 functionalities that can be garnered from significantly expand the development of a E [email protected] HUDS. Firstly, the physicists have utilised finite new material for next-generation concepts for difference time domain and band structure advanced photonic devices. From Steinhardt’s Paul J Steinhardt is the Albert Einstein computer simulations to demonstrate that perspective, the efforts have important Professor in Science and Director of the waveguide architectures of arbitrary shape can applications in “optical telecommunications, Princeton Center for Theoretical Science be constructed in hyperuniform disordered energy harvesting, non-linear optics and at Princeton University. His research spans photonic solids – something that is not improved light sources”. problems in particle physics, astrophysics, cosmology, geophysics and condensed matter physics, including the introduction and exploration of quasicrystal properties and HUDS.

Salvatore Torquato is Professor of Chemistry at Princeton University. He is broadly interested in the fundamental microscopic understanding of the structure and bulk properties of condensed matter via statistical mechanics. His current work focuses on self-assembly theory, particle packings, hyperuniform materials, glasses, quasicrystals, optimisation of materials and cancer modeling.

Marian Florescu is Senior Lecturer at the University of Surrey. His research interests include nanophotonics, implementations of linear optical quantum computing and spintronics. His current activities are focused on non- In a hyperuniform distribution of points, the number of points within a circle varies according to where you the place crystallographic PBG materials, thermal the circle by an amount that depends on its circumference, as shown for the case of a crystal array of points (left); radiation in photonic materials and quantum for a truly random distribution (middle), on its area; for HUDS (right), despite being disordered and isotropic like the optics in structured photonic reservoirs. random distribution, the variance depends on the circumference, the same result obtained for crystal.