Query: Fundamental scaling laws in nanophotonics

Candidate papers:

abstract: The success of information technology has clearly demonstrated that miniaturization often leads to unprecedented performance, and unanticipated applications. This hypothesis of "smaller is better" has motivated optical engineers to build various nanophotonic devices, although an understanding leading to fundamental scaling behavior for this new class of devices is missing. Here we analyze scaling laws for optoelectronic devices operating at micro and nanometer length scale. We show that optoelectronic device performance scales non monotonically with device length due to the various device tradeoffs, and analyze how both optical and electrical constrains influence device power consumption and operating speed. Specifically, we investigate the direct influence of scaling on the performance of four classes of photonic devices, namely laser sources, electro optic modulators, photodetectors, and all optical switches based on three types of optical resonators; microring, Fabry Perot cavity, and plasmonic metal nanoparticle. Results show that while microrings and Fabry Perot cavities can outperform plasmonic cavities at larger length scales, they stop working when the device length drops below 100 nanometers, due to insufficient functionality such as feedback (laser) index modulation (modulator) absorption (detector) or field density (optical switch) Our results provide a detailed understanding of the limits of nanophotonics, towards establishing an opto electronics roadmap, akin to the International Technology Roadmap for Semiconductors.
author_names: Ke Liu

Shuai Sun

Arka Majumdar

Volker J Sorger
title: Fundamental Scaling Laws in Nanophotonics
venue: Scientific reports
year: 2016

abstract: We show that nanophotonic device performance scales non monotonically with critical length and define the metric [Speed (Energy/bit x Footprint) to assess the quality of optoelectronic link performance based on both optical and electrical tradeoffs.
author_names: Ke Liu

Shuai Sun

Arka Majumdar

Volker J Sorger
title: Fundamental Physical Scaling Laws of Nanophotonics
year: 2017

abstract: Thermal radiation plays an increasingly important role in many emerging energy technologies, such as thermophotovoltaics, passive radiative cooling and wearable cooling clothes [1] One of the fundamental constraints in thermal radiation is the Stefan Boltzmann law, which limits the maximum power of far field radiation to P0 sT4S, where s is the Boltzmann constant, S and T are the area and the temperature of the emitter, respectively (Fig. 1a) In order to overcome this limit, it has been shown that near field radiations could have an energy density that is orders ofmagnitude greater than the StefanBoltzmann law [2 7] Unfortunately, such near field radiation transfer is spatially confined and cannot carry radiative heat to the far field. Recently, a new concept of thermal extraction was proposed [8] to enhance far field thermal emission, which, conceptually, operates on a principle similar to oil immersion lenses and light extraction in light emitting diodes using solid immersion lens to increase light output [62].Thermal extraction allows a blackbody to radiate more energy to the far field than the apparent limit of the Stefan Boltzmann lawwithout breaking the second law of thermodynamics. Thermal extraction works by using a specially designed thermal extractor to convert and guide the near field energy to the far field, as shown in Fig. 1b. The same blackbody as shown in Fig. 1a is placed closely below the thermal extractor with a spacing smaller than the thermal wavelength. Thenear field coupling transfers radiative energy with a density greater than sT4. The thermal extractor, made from transparent and high index or structured materials, does not emit or absorb any radiation. It transforms the near field energy and sends it toward the far field. As a result, the total amount of far field radiative heat dissipated by the sameblackbody is greatly enhanced above SsT4, where S is the area of the emitter. This paper will review the progress in thermal extraction. It is organized as follows. In Section 1, we will discuss the theory of thermal extraction [8] In Section 2, we review an experimental implementation based on natural materials as the thermal extractor [8] Lastly, in Section 3, we review the experiment that uses structured metamaterials as thermal extractors to enhance optical density of states and far field emission [9] Figure 1: Schematic of radiative cooling. (Left) Emitter without thermal extractor. (Right) Radiation power of emitter with thermal extractor is larger than that on the left. 1 Thermal Extraction Theory We start by considering the classical construction of an ideal blackbody emitter: a small opening in a cavity as shown in Fig. 2. The cavity is filled with transparent dielectric medium that has a refractive index ni as shown in Fig. 2a. Outside the cavity is vacuum. Inside the cavity, the sidewalls are made of diffusive reflector that also absorbs light. Any light that enters through the open areawill bounce back and forth between the sidewalls and eventually get fully absorbed by the cavity. Here we assume perfect antireflection at the opening of the cavity. The cavity's temperature is T and its opening area has an area of S. The opening area is completely dark with a unity emissivity. Wewill investigate the thermal emissionwhen the cavity is filled bymaterials of different refractive indices ni. As we varyni, the thermal radiation intensity inside the cavity Yixuan Tan, Zongfu Yu: Department of Electrical and Computer Engineering, University of Wisconsin, Wisconsin, Madison, 53706, USA Baoan Liu, Sheng Shen: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, 15213, USA 2 Yixuan Tan, Baoan Liu, Sheng Shen, and Zongfu Yu scales as ni However, the cavity always has the same farfield thermal emission with an emitted power of sT4S [37] This is because the total internal reflection at the opening of the cavity prevents a significant portion of the internal thermal radiation from leaving the cavity. The resulting thermal emission to the far field vacuum always has the same profile independent of refractive index ni. To extract more radiation power from this type of a structure, Yu, et al. [8] proposed to place a hemispherical dome to cover the cavity, as shown in Fig. 2 b. Here the dome has an index ne. It enlarges the critical angle for totally internal reflection at the cavity opening and thus enablesmore thermal radiationmodes inside the cavity to escape. Importantly, the dome itself is assumed to be transparent, so that it neither emits nor absorbs any thermal radiation. Figure 2: Schematic and actual demonstration of thermal extraction. (a) Emitter formed by an open area (dark red surface) of an absorptive cavity. The cavity can be filled with a transparent dielectric of refractive index ni. (b) Thermal extraction using a hemispherical dome placed at the opening of the cavity. The dome is transparent and does not emit or absorb any thermal radiations, and has a refractive index ne. Emission cone (white) of the thermal radiation inside the dome is shown. (c, d) [8] Experiment set up. A ray tracingmethod can be used to calculate the thermal emission from the geometry shown in Fig. 2b. It is assumed that the opening of the cavity has a circular shape of radius r and the dome has a radius R such that R ner, which ensures that any light reaching the surface of the dome can escape to the far field vacuum. Under such conditions, a light ray originating from the open area S, has an incident angle less than the total internal reflection angle ph sin 1 1 ne (Fig. 2b, solid arrows) at the curved interface between the dome and the outside vacuum. It can be shown that the total emission power is P nesTpr (if ni ne) ni sT4pr2 (if ni ne) (1) Fig. 3 shows the thermal radiation as a function of the refractive index of the dome ne. The total radiation power from an empty cavity (ni= 1 dashed line in Fig. 3) does not change as a function of ne, while the power from the filled cavity (solid line in Fig. 3) increases as ne increases until ne ni. With the assistance of the thermal extraction, the filled cavity can emit up to ni SsT4 to far field vacuum, ni times of the radiated power without the thermal extractor. The internal density of the state of the thermal body must be higher than that of the extraction device in order to achieve the maximum effect of the enhanced thermal emission. Figure 3: Enhancement of far field radiation power as a function of the refractive index of the dome ne. Enhancement is compared with sT4S. The structure for enhancement is shown in Fig. 2b. Solid line: Filled cavity with ni 3. Dashed line: Empty cavity with ni 1 [8] The distribution of thermal radiation on the surface of the dome can be calculated with a schematic shown in Fig. 4a. For a small area A on the surface of the dome, the thermal radiation power it receives from the cavity is
author_names: Yixuan Tan

Bao'an Liu

Sheng Shen

Zongfu Yu
title: Smart nanophotonics for renewable energy and sustainability
year: 2016

abstract: Inertial microfluidics has attracted significant attention in recent years due to its superior benefits of high throughput, precise control, simplicity, and low cost. Many inertial microfluidic applications have been demonstrated for physiological sample processing, clinical diagnostics, and environmental monitoring and cleanup. In this review, we discuss the fundamental mechanisms and principles of inertial migration and Dean flow, which are the basis of inertial microfluidics, and provide basic scaling laws for designing the inertial microfluidic devices. This will allow end users with diverse backgrounds to more easily take advantage of the inertial microfluidic technologies in a wide range of applications. A variety of recent applications are also classified according to the structure of the microchannel: straight channels and curved channels. Finally, several future perspectives of employing fluid inertia in microfluidic based cell sorting are discussed. Inertial microfluidics is still expected to be promising in the near future with more novel designs using various shapes of cross section, sheath flows with different viscosities, or technologies that target micron and submicron bioparticles.
author_names: Ga-Yeong Kim

Jong-in Han

Je Kyun Park
title: Inertial Microfluidics Based Cell Sorting
venue: BioChip Journal
year: 2018

abstract: At the National Observatory in Washington D.C. time is measured by averaging the times of an uncoupled ensemble. The measurements show a scaling law for phase error reduction as, where is the number of crystals in the ensemble. Analytical and computational works show that certain patterns of collective behavior produced by a network of nonlinear oscillators leads to optimal phase error that scales down as. In this talk we use symmetry based methods to classify all possible patterns of oscillations, and their stability properties. Then we show why, among all possible patterns, a traveling wave, in which consecutive oscillators are out of phase by, yields the best phase error reduction. Finally, we prove, analytically, that is the fundamental limit of of phase error reduction that can be obtained with a network of nonlinear oscillators of any type, not just crystals.
author_names: Antonio Palacios

Pietro-Luciano Buono

Visarath In

Patrick Longhini
title: Coupled Crystal Oscillator System and Timing Device
year: 2019

abstract: Modern nanophotonic and meta optical devices utilize a tremendous number of structural degrees of freedom to enhance light matter interactions. A fundamental question is how large such enhancements can be. We develop an analytical framework to derive upper bounds to single frequency electromagnetic response, across near and far field regimes, for any materials, naturally incorporating the tandem effects of material and radiation induced losses. Our framework relies on a power conservation law for the polarization fields induced in any scatterer. It unifies previous theories on optical scattering bounds and reveals new insight for optimal nanophotonic design, with applications including far field scattering, near field local density of states engineering, optimal wavefront shaping, and the design of perfect absorbers. Our bounds predict strikingly large minimal thicknesses for arbitrarily patterned perfect absorbers, ranging from 50 100 nm for typical materials at visible wavelengths to micrometer scale thicknesses for polar dielectrics at infrared wavelengths. We use inverse design to discover metasurface structures approaching the minimum thickness perfect absorber bounds.
author_names: Zeyu Kuang

Lang Zhang

Owen D Miller
title: Maximal single frequency electromagnetic response
year: 2020

abstract: Modern nanophotonic and meta optical devices utilize a tremendous number of structural degrees of freedom to enhance light matter interactions. A fundamental question is how large such enhancements can be. We develop an analytical framework to derive upper bounds to single frequency electromagnetic response, across near and far field regimes, for any materials, naturally incorporating the tandem effects of material and radiation induced losses. Our framework relies on a power conservation law for the polarization fields induced in any scatterer. It unifies previous theories on optical scattering bounds and reveals new insight for optimal nanophotonic design, with applications including far field scattering, near field local density of states engineering, optimal wavefront shaping, and the design of perfect absorbers. Our bounds predict strikingly large minimal thicknesses for arbitrarily patterned perfect absorbers, ranging from 50 100 nm for typical materials at visible wavelengths to micrometer scale thicknesses for polar dielectrics at infrared wavelengths. We use inverse design to discover metasurface structures approaching the minimum thickness perfect absorber bounds.
author_names: Zeyu Kuang

Lang Zhang

Owen D Miller
title: Maximal single frequency electromagnetic response
year: 2020

abstract: In this thesis, we explore the interaction of thermal radiation with nano scale structures. First, we introduce the concept of radiative energy transfer between two objects of different temperatures in the near field, and theoretically argue that the radiation tunneling of evanescent surface modes can enable energy transfer that is orders of magnitude stronger than the energy transfer in the far field. Specifically, we develop a new computational approach based on a finite difference time domain (FDTD) method that incorporates the Langevin approach to Brownian motion which enables calculations of heat transfer for arbitrary geometries and materials. Second, we study the near field heat transfer between two sheets of graphene and show that thermally excited plasmon polariton modes can strongly mediate, enhance, and tune the energy exchange in this system. We predict maximum transfer at low doping and for plasmons in two graphene sheets in resonance, with orders of magnitude enhancement over the Stefan Boltzmann law. Third, we develop the concept of a near field thermophotovoltaic (NFTPV) system, and analyze several different implementations that use plasmonic materials as thermal emitters. In particular, we quantify the properties of an optimal near field photovoltaic cell, argue that large plasmonic losses can contrary to intuition be helpful in enhancing the overall heat transfer, and propose and develop the concept of graphene as a tunable thermal emitter for a NFTPV system. Fourth, we tailor the far field thermal emission from objects at high temperatures and experimentally demonstrate a method where the emission spectrum is controlled on the cold side by implementing a nano layer structure that surrounds the hot emitter and recycles unwanted emission. We find that this approach can enable lighting sources with luminous efficiencies close to the fundamental limit for lighting applications. Finally, we study opto thermal effects in asymmetric nanoparticles. Specifically, we show that a type of metal dielectric (Janus) particle in uniform light field exhibits a new class of stable rotational dynamics. We demonstrate (in a simulation) opto thermal guiding of a composite asymmetric particle by switching the light beam frequency, without regard to the direction or the shape of the light beam.
author_names: Ognjen Ilic
title: Nanophotonics for tailoring the flow of thermal electromagnetic radiation
year: 2015

abstract: Self organized criticality emerges in dynamical complex systems driven out of equilibrium, and characterizes a wide range of classical phenomena in physics, geology and biology. However, for decades now, it remains a fundamental open question whether this broad property also finds a place in the quantum regime. In the talk, we shall present the first example of quantum self organized criticality, emerging from quantum fluctuations and controlled by quantum coherence. We shall introduce a many body quantum coherently driven nanophotonic system where heavy photons interact in the presence of active nonlinearities. In this system, we shall show how quantum self organized criticality emerges in an inherently new type of light localization, arising from two first order phase transitions and being robust to dissipation, fluctuations and many body interactions. The observed localization exhibits emergence of scale invariant power laws and absence of finely tuned control parameters. In analogy with the regime of quantum criticality at Tc 0 in equilibrium static systems, we find that for our nonequilibrium dynamical system there exists a range of parameters for which the effective critical 'temperature' drops to zero, at which point we enter a fundamentally new regime of phase transitions the quantum self organized critical regime. We shall also approach the problem from a thermodynamic and information theory perspective, deriving the multidimensional state vector Fokker Planck (FP) equation for the distribution function of our problem, applying the maximum information entropy principle to make unbiased estimates on the probability distribution of microscopic states of our active nanosystem, and finally determining and analyzing the information gain and efficiency of the complex nanosystem close to its critical points.
author_names: Kosmas L Tsakmakidis

Pankaj Kumar Jha

Xiang Zhang

Hatice Altug

Robert W Boyd

Ganapathi S Subramania

Stavroula Foteinopoulou
title: Quantum self organized criticality and nonequilibrium light localization (Conference Presentation)
year: 2017

abstract: This thesis describes and characterizes a setup to conduct experiments combining the fields of cold atoms and nanophotonics. Furthermore, a series of numerical simulations is employed to deepen of atom transport under experimentally realistic conditions. The study of cold atoms is usually fundamental in nature and a very clean approach to investigate the laws of physics. High purity samples of atoms are cooled down to millikelvins or microkelvins. The potential landscape for the atoms can be carefully controlled using lasers and/or magnetic fields. Since the atoms' responses to electric, magnetic or electromagnetic fields are known with very high fidelity, any deviations to the state the atoms are prepared in can be precisely measured. Nanophotonics is the study of light close to or beyond the diffraction limit. In this region the field like nature of light starts to play a role. By confining light in sub wavelength sized structures, high peak intensities can be achieved, giving rise to exciting non linear optics phenomena. The strong field gradient that can be created allows, for instance, precise spectroscopy measurements, phase sensitive sub wavelength microscopy, as well as producing highly receptive sensing devices. Combining cold atoms and nanophotonics creates strong synergy effects. It gives access to strong coupling of light and matter. The scalability of nanophotonics now extends to atomic physics. Atoms can be trapped, coupled and manipulated at very small length scales, and in large numbers. Moreover, the potential landscape for atoms is highly customizable. The rubidium isotope 87 is used in this setup. A cloud of rubidium atoms is gathered and cooled in a two dimensional magneto optical trap (MOT) Since the atoms are only cooled in two dimensions, they are free to escape in the third dimension and load a following three dimensional MOT. The atoms are now cooled further, compressed and loaded into an optical dipole trap. This dipole trap transports the atoms close to a sample inside the vacuum chamber. A moving optical lattice, or optical conveyor belt, brings the atoms then close to the sample surface. Now experiments can be conducted, studying the interaction of cold atoms and strongly confined light. The atom transport down to the sample surface shows some unexpected behaviour: the atoms seem to spread through the optical lattice during transport. A combination of microscopic and macroscopic numerical simulations, including genetic algorithms, are used to deepen our understanding of the underlying physics. This also allows us to get access to experimental variables that cannot be directly obtained.
author_names: Bernd Mussmann
title: A Versatile Atom Transport Apparatus for Photonics
year: 2016