# Physics - Optics Publications (50)

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## Physics - Optics Publications

We describe a versatile mechanism that provides tight-binding models with an enriched, topologically nontrivial bandstructure. The mechanism is algebraic in nature, and leads to tight-binding models that can be interpreted as a non-trivial square root of a parent lattice Hamiltonian---in analogy to the passage from a Klein-Gordon equation to a Dirac equation. In the tight-binding setting, the square-root operation admits to induce spectral symmetries at the expense of broken crystal symmetries. Read More

Nanoscale mechanical oscillators are sensitive to a wide range of forces, and are the subject of studies into fundamental quantum physics. They can be used for mass detection at the single proton level, position measurements to the quantum limit, and they have found application in genetics, proteomics, microbiology and studies of DNA. Their sensitivity is limited by dissipation to the environment, which reduces the mechanical quality factor $Q_{\rm m}$. Read More

The mathematical notion of spectral singularity admits a description in terms of purely outgoing solutions of a corresponding linear wave equation. This leads to a nonlinear generalization of this notion for nonlinearities that are confined in space. We examine the nonlinear spectral singularities in arbitrary TE and TM modes of a mirrorless slab laser that involves a weak Kerr nonlinearity. Read More

We have detected a second-order nonlinear optical response from aggregates of the ampholytic megamolecular polysaccharide sacran extracted from cyanobacterial biomaterials, by using optical second harmonic generation (SHG) microscopy. The SHG images of sacran cotton-like lump, fibers, and cast films showed SHG intensity microspots of several tens of micrometers in size. The dependence of the SHG spot intensity on an excitation light polarization angle was observed to illustrate sacran molecular orientation in these microdomains. Read More

Accurate modeling of light scattering from nanometer scale defects on Silicon wafers is critical for enabling increasingly shrinking semiconductor technology nodes of the future. Yet, such modeling of defect scattering remains unsolved since existing modeling techniques fail to account for complex defect and wafer geometries. Here, we present results of laser beam scattering from spherical and ellipsoidal particles located on the surface of a silicon wafer. Read More

We describe nonlinear Bessel vortex beams as localized and stationary solutions with embedded vorticity to the nonlinear Schr\"odinger equation with a dissipative term that accounts for the multi-photon absorption processes taking place at high enough powers in common optical media. In these beams, power and orbital angular momentum are permanently transferred to matter in the inner, nonlinear rings, at the same time that they are refueled by spiral inward currents of energy and angular momentum coming from the outer linear rings, acting as an intrinsic reservoir. Unlike vortex solitons and dissipative vortex solitons, the existence of these vortex beams does not critically depend on the precise form of the dispersive nonlinearities, as Kerr self-focusing or self-defocusing, and do not require a balancing gain. Read More

Various metals (Ag, Al, Au, Bi, Cu), polymers (polyvinylpyrrolidone, polystyrene), and electrically conductive polymers (polyacetylene, polyaniline, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) were subjected to a particle swarm optimizer inboth the planar and grating configuration to optimize conditions which supported surface plasmon resonances (SPR) for chemical sensing. The objective functions for these configurations were based on absorption peak depth, full width at half maximum, or the enhancement factor (planar). Simple logic gates were constructed for both configurations which assessed if a lossy region was plasmonic by several figures of merit. Read More

**Affiliations:**

^{1}L2C

Ultrasound-modulated optical tomography (UOT) is a technique that images optical contrast deep inside scattering media. Heterodyne holography is a promising tool able to detect the UOT tagged photons with high efficiency. In this work, we describe theoretically the detection of the tagged photon in heterodyne holography based UOT, show how to filter the untagged photon, and discuss the effect of shot noise. Read More

We propose a method to generate path-entangled $N00N$-state photons from quantum dots (QDs) and coupled nanocavities. In the systems we considered, cavity mode frequencies are tuned close to the biexciton two-photon resonance. Under appropriate conditions, the system can have the target $N00N$ state in the energy eigenstate, as a consequence of destructive quantum interference. Read More

Photography usually requires optics in conjunction with a recording device (an image sensor). Eliminating the optics could lead to new form factors for cameras. Here, we report a simple demonstration of imaging using a bare CMOS sensor that utilizes computation. Read More

Quantum coherence, which quantifies the superposition properties of a quantum state, plays an indispensable role in quantum resource theory. A recent theoretical work [Phys. Rev. Read More

We present a self-consistent quantum optics approach to calculating the surface enhanced Raman spectrum of molecules coupled to arbitrarily shaped plasmonic systems. Our treatment is intuitive to use and provides fresh analytical insight into the physics of the Raman scattering near metallic surfaces and can be applied to a wide range of geometries including resonators, waveguides, as well as hybrid photonic-plasmonic systems. Our general theory demonstrates that the detected Raman spectrum originates from an interplay between nonlinear light generation and propagation. Read More

Breaking reciprocity associated with wave propagation is a fundamental challenge across a wide range of physical systems in electromagnetics, optics, and acoustics. In contrast to established magneto-optic methods, recent efforts have focused instead on inducing nonreciprocity using time-varying biases such as synchronized spatiotemporal modulation of resonators and waveguides. To date, the elements that couple these time-varying resonator and waveguide modes are always considered to be reciprocal, and the nonreciprocal transfer functions achieved by these systems have been mostly limited to narrow-band resonances. Read More

Quantum erasers with paths in the form of physical slits have been studied extensively and proven instrumental in probing wave-particle duality in quantum mechanics. Here we replace physical paths (slits) with abstract paths of orbital angular momentum (OAM). Using spin-orbit hybrid entanglement of photons we show that the OAM content of a photon can be erased with a complimentary polarization projection of one of the entangled pair. Read More

We analyze the stimulated (emission/absorption) interaction of an electron quantum wavepacket with coherent radiation, using perturbation theory and numerical solution of Schrodinger equation. The analysis applies to a wide class of free electron radiative interaction schemes, and exemplified for Smith-Purcell radiation. Though QED theory and experiments indicate that spontaneous emission of radiation by a free electron is independent of its dimensions, we show that wavepacket dimensions do affect the stimulated radiative interaction in a certain range. Read More

Polarization-based filtering in fiber lasers is well-known to enable spectral tunability and a wide range of dynamical operating states. This effect is rarely exploited in practical systems, however, because optimization of cavity parameters is non-trivial and evolves due to environmental sensitivity. Here, we report a genetic algorithm-based approach, utilizing electronic control of the cavity transfer function, to autonomously achieve broad wavelength tuning and the generation of Q-switched pulses with variable repetition rate and duration. Read More

In this Letter we study theoretically the interaction of optical waves in nonlinear dynamical medium, i.e. medium with relaxation. Read More

A ~545 mW single-frequency tunable 520 nm green laser has been demonstrated using a periodically-poled potassium titanyl phosphate (PPKTP) bulk crystal based on single-pass third-harmonic generation (THG) of a 1560 nm laser via single-pass second-harmonic generation (SHG) followed by single-pass sum-frequency generation (SFG). In single-pass SHG, two cascaded periodically-poled magnesium-oxide-doped lithium niobate (PPMgO:LN) crystals were used, and ~3.5 W 780. Read More

We have investigated mixed-gap vector solitons involving incoherently coupled fundamental and dipole components in a parity-time (PT) symmetric lattice with saturable nonlinearity. For the focusing case, vector solitons emerge from the semi-infinite and the first finite gaps, while for the defocusing case, vector solitons emerge from the first finite and the second finite gaps. For both cases, we find that stronger saturable nonlinearity is relative to sharper increase/decrease of soliton power with propagation constant and to narrower existence domain of vector solitons. Read More

VIPA-based spectrometers have enabled rapid Brillouin spectrum measurements and current designs of multi-stage VIPA spectrometers offer enough spectral extinction to probe transparent tissue, cells and biomaterials. However, in highly scattering media or in the presence of strong back-reflections, such as at interfaces between materials of different refractive indices, VIPA-based Brillouin spectral measurements are limited. While several approaches to address this issue have recently been pursued, important challenges remain. Read More

Liquid crystals allow for the real-time control of the polarization of light. We describe and provide some experimental examples of the types of general polarization transformations, including universal polarization transformations, that can be accomplished with liquid crystals in tandem with fixed waveplates. Implementing these transformations with an array of liquid crystals, e. Read More

Fringe-projection profilometry with 1 camera and 1 fringe-projector is a well-known and widely used technique in optical metrology. Spatial-frequency multiplexing interferometry with several spatial-carriers having non-overlapping spatial-spectra is also well known and productive in optical metrology. In this paper we propose temporal-multiplexing phase-shifting interferometry applied to profilometry. Read More

Graded index media whose electric susceptibility satisfies the spatial Kramers-Kronig relations are known to be one-way reflectionless to electromagnetic radiation, for all angles of incidence. We demonstrate how a family of these media, in addition to being reflectionless, also have negligible transmission. To this end, we discuss how the transmission coefficient for the propagation of waves through a medium whose permittivity is built from poles in the complex position plane, with residues that sum to infinity, can be controlled by tuning the positions and residues of the poles. Read More

The article reports on light enhancement by structural resonances in linear periodic arrays of identical dielectric elements. As the basic elements both spheres and rods with circular cross section have been considered. In either case, it has been demonstrated that high-$Q$ structural resonant modes originated from bound states in the continuum enable near-field amplitude enhancement by factor of $10$--$25$ in the red-to-near infrared range in lossy silicon. Read More

While experiments with one or two quantum emitters have become routine in various laboratories, scalable platforms for efficient optical coupling of many quantum systems remain elusive. To address this issue, we report on chip-based systems made of one-dimensional subwavelength dielectric waveguides (nanoguides) and polycyclic aromatic hydrocarbon molecules. After discussing the design and fabrication requirements, we present data on coherent linear and nonlinear spectroscopy of single molecules coupled to a nanoguide mode. Read More

Here, the Abraham-Minkowski controversy on the correct definition of the light momentum in a macroscopic medium is revisited with the purpose to highlight that an effective medium formalism necessarily restricts the available information on the internal state of a system, and that this is ultimately the reason why the dilemma has no universal solution. Despite these difficulties, it is demonstrated that in the limit of no material absorption and under steady-state conditions, the time-averaged light momentum is unambiguously determined by the Abraham result, both for bodies at rest and for circulatory flows of matter. The implications of these findings are discussed in the context of quantum optics of moving media, and we examine in detail the fundamental role of the Minkowski momentum in such a context. Read More

Integrated polarimetric receivers have the potential to define a new generation of lightweight, high-performance instrumentation for remote sensing. To date, on-chip polarization-selective devices such as polarizing beam-splitters have yet to even approach the necessary performance, due to fundamental design limitations. Here, we propose, simulate and experimentally demonstrate a method for realizing spatially-mapped birefringence onto integrated photonic circuits, deemed topographically anisotropic photonics. Read More

Quantum frequency conversion in nonlinear optical media is a powerful tool for temporal-mode selective manipulation of light. Recent attempts at achieving high mode selectivities and/or fidelities have had to resort to multi-dimensional optimization schemes to determine the system's natural Schmidt modes. Certain combinations of relative-group velocities between the relevant frequency bands, medium lengths, and temporal pulse widths have been known to achieve good selectivity for temporal modes that are nearly identical to pump pulse shapes, even at high pump powers. Read More

Despite its attractive features, Congruent-melted Lithium Niobate (CLN) suffers from Photo-Refractive Damage (PRD). This light-induced refractive-index change hampers the use of CLN when high-power densities are in play, a typical regime in integrated optics. The resistance to PRD can be largely improved by doping the lithium-niobate substrates with magnesium oxide. Read More

We demonstrate that pulses of linear physical systems, weakly perturbed by nonlinear dissipation, exhibit soliton-like behavior in fast collisions. The behavior is demonstrated for linear waveguides with weak cubic loss and for systems described by linear diffusion-advection models with weak quadratic loss. We show that in both systems, the expressions for the collision-induced amplitude shifts due to the nonlinear loss have the same form as the expression for the amplitude shift in a fast collision between two optical solitons in the presence of weak cubic loss. Read More

We report a new electromagnetic mode at the interface between two planar surfaces and demonstrate an open boundary structure capable of confining and guiding waves along a one-dimensional line object. The mode is determined by complementary isotropic impedance boundary conditions and is experimentally verified using patterned conductor surfaces. The line wave possesses a singular field enhancement, unidirectional propagation, wide bandwidth and tunable field confinement properties, which may advance applications of topological photonic insulators. Read More

Novel hollow-core THz waveguides featuring hyperuniform disordered reflectors are proposed, fabricated, and characterized. The reflector comprise aperiodically positioned dielectric cylinders connected with dielectric bridges. The proposed waveguides are fabricated using a 3D stereolithography printer. Read More

The newly emerging field of wave front shaping in complex media has recently seen enormous progress. The driving force behind these advances has been the experimental accessibility of the information stored in the scattering matrix of a disordered medium, which can nowadays routinely be exploited to focus light as well as to image or to transmit information even across highly turbid scattering samples. We will provide an overview of these new techniques, of their experimental implementations as well as of the underlying theoretical concepts following from mesoscopic scattering theory. Read More

A range of unique capabilities in optical and microwave signal processing have been demonstrated using stimulated Brillouin scattering. The desire to harness Brillouin scattering in mass manufacturable integrated circuits has led to a focus on silicon-based material platforms. Remarkable progress in silicon-based Brillouin waveguides has been made, but results have been hindered by nonlinear losses present at telecommunications wavelengths. Read More

**Authors:**Daming Wang

^{1}, Longsheng Wang

^{2}, Tong Zhao

^{3}, Hua Gao

^{4}, Yuncai Wang

^{5}, Xianfeng Chen

^{6}, Anbang Wang

^{7}

**Affiliations:**

^{1}Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan, China,

^{2}Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan, China,

^{3}Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan, China,

^{4}Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan, China,

^{5}Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan, China,

^{6}School of Electronic Engineering, Bangor University, Bangor, UK,

^{7}Key Laboratory of Advanced Transducers and Intelligent Control System, Ministry of Education, Taiyuan University of Technology, Taiyuan, China

**Category:**Physics - Optics

Time delay signature (TDS) of a semiconductor laser subject to dispersive optical feedback from a chirped fiber Bragg grating (CFBG) is investigated experimentally and numerically. Different from mirror, CFBG provides additional frequency-dependent delay caused by dispersion, and thus induces external-cavity modes with irregular mode separation rather than a fixed separation induced by mirror feedback. Compared with mirror feedback, the CFBG feedback can greatly depress and even eliminate the TDS, although it leads to a similar quasi-period route to chaos with increases of feedback. Read More

The small correction volume for conventional wavefront shaping methods limits their applications in biological imaging through scattering media. We demonstrate large volume wavefront shaping through a scattering layer with a single correction by conjugate adaptive optics and remote focusing (CAORF). The remote focusing module can keep the conjugation between the AO and scattering layer during three-dimensional scanning. Read More

Optical microcavities are compact, often chip-based devices, that are essential in technologies spanning frequency metrology to biosensing. They have also enabled new science in quantum information and cavity optomechanics. Performance requirements in subjects like cavity-QED and sensing have long placed emphasis on low-optical-loss (high-Q-factor) micrometer-scale resonators. Read More

We consider a semi-infinite dielectric with multiple spatially dispersive resonances in the susceptibility. The effect of the boundary is described by an arbitrary reflection coefficient for polarization waves in the material at the surface, with specific values corresponding to various additional boundary conditions (ABCs) for Maxwell's equations. We derive exact expressions for the electromagnetic reflection and transmission coefficients and present the results for a variety of materials with multiple exciton bands. Read More

We analyze the stability of a non-Hermitian coupler with respect to modulational inhomogeneous perturbations in the presence of unbalanced gain and loss. At the parity-time (PT) symmetry point the coupler is unstable. Suitable symmetry breakings lead to an asymmetric coupler, which hosts nonlinear supermodes. Read More

Molecules are the most demanding quantum systems to be simulated by quantum computers because of their complexity and the emergent role of quantum nature. The recent theoretical proposal of Huh et al. (Nature Photon. Read More

The ability to tailor a coherent surface plasmon polariton (SPP) field is an important step towards a number of new opportunities for a broad range of nanophotonic applications such as sensing [1,2], nano-circuitry [3,4], optical data storage [5,6], super-resolution imaging [7,8], plasmonic tweezers [9,10] and in-plane communications [11]. Scanning a converging SPP spot or designing SPP profiles using an ensemble of spots have both been demonstrated previously [12-14]. SPPs, however, are normally excited by intense, coherent light sources-lasers. Read More

We develop a general microscopic theory describing the phonon-induced decoherence of photons emitted by quantum dots placed in various photonic structures. The decoherence is found to depend fundamentally on the dimensionality of the structure resulting in vastly different performance for quantum dots embedded in a nano-cavity (0D), waveguide (1D), slab (2D), or bulk medium (3D). In bulk, we find a striking temperature dependence of the dephasing rate scaling as $T^{11}$ implying that phonons are effectively 'frozen out' for $T \lesssim 4\mathrm{K}$. Read More

We study the effect of off-resonance plasmon modes on spaser action in plasmonic systems with gain. We show that mode mixing originates from inhomogeneity of gain distribution near the metal surface and leads to an upward shift of spaser frequency and population inversion threshold. This effect is similar, albeit significantly weaker, to quenching of plasmon-enhanced fluorescence of a single emitter near metal nanostructure due to excitation of nonresonant modes with wide spectral band. Read More

Formation of a bright-field microscopic image of a transparent phase object is described in terms of elementary geometrical optics. Our approach is based on the premise that image replicates the intensity distribution (real or virtual) at the front focal plane of the objective. The task is therefore reduced to finding the change in intensity at the focal plane caused by the object. Read More

**Authors:**D. G. Matei

^{1}, T. Legero

^{2}, S. Häfner

^{3}, C. Grebing

^{4}, R. Weyrich

^{5}, W. Zhang

^{6}, L. Sonderhouse

^{7}, J. M. Robinson

^{8}, J. Ye

^{9}, F. Riehle

^{10}, U. Sterr

^{11}

**Affiliations:**

^{1}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany,

^{2}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany,

^{3}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany,

^{4}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany,

^{5}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany,

^{6}JILA, NIST and University of Colorado, Boulder CO, USA,

^{7}JILA, NIST and University of Colorado, Boulder CO, USA,

^{8}JILA, NIST and University of Colorado, Boulder CO, USA,

^{9}JILA, NIST and University of Colorado, Boulder CO, USA,

^{10}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany,

^{11}Physikalisch-Technische Bundesanstalt, Braunschweig, Germany

We report on two ultrastable lasers each stabilized to independent silicon Fabry-P\'erot cavities operated at 124 K. The fractional frequency instability of each laser is completely determined by the fundamental thermal Brownian noise of the mirror coatings with a flicker noise floor of $4 \times 10^{-17}$ for integration times between 0.8 s and a few tens of seconds. Read More

In this paper, we introduce an alternative representation of the electromagnetic field scattered from a homogeneous sphere coated with a homogeneous layer of uniform thickness. Specifically, we expand the scattered field using a set of modes that are independent of the permittivity of the coating, while the expansion coefficients are simple rational functions of the permittivity. The theory we develop represents both a framework for the analysis of plasmonic and photonic modes and a straightforward methodology to design the permittivity of the coating to pursue a prescribed tailoring of the scattered field. Read More

**Authors:**Filippus S. Roux

Uncertainties in the frequency parameters of a frequency comb laser, causes it to represent a mixed quantum state. The formulation of such a quantum state is compounded by the fact that it contains both particle-number degrees of freedom and temporal degrees of freedom. Here we develop a formalism in terms of which such a mixed quantum state can be expressed. Read More

We theoretically investigate the generation of intense keV attosecond pulses in an orthogonally polarized multicycle midinfrared two-color laser field. It is demonstrated that multiple continuum-like humps, which have a spectral width of about twenty orders of harmonics and an intensity of about one order higher than adjacent normal harmonic peaks, are generated under proper two-color delays, owing to the reduction of the number of electron-ion recollisions and suppression of inter-half-cycle interference effect of multiple electron trajectories when the long wavelength midinfrared driving field is used. Using the semiclassical trajectory model, we have revealed the two-dimensional manipulation of the electron-ion recollision process, which agrees well with the time frequency analysis. Read More

We explore the dynamics of spontaneous breakdown of mirror symmetry in a pair of identical optomechanical cavities symmetrically coupled to a waveguide. Large optical intensities enable optomechanically-induced nonlinear detuning of the optical resonators, resulting in a pitchfork bifurcation. We investigate the stability of this regime and explore the possibility of inducing multistability. Read More

We show that a small linear refractive index leads to the violation of standard approximations in nonlinear optics. Consequently, the conventional equation for the intensity-dependent refractive index becomes inapplicable in epsilon-near-zero and low-index media, even only in the presence of third-order effects. In indium tin oxide, we find that the $\chi^{(3)}$, $\chi^{(5)}$ and $\chi^{(7)}$ contributions to refraction eclipse the linear term; thus, the nonlinear response can no longer be interpreted as a perturbation in these materials. Read More