This PDF file contains the front matter associated with SPIE Proceedings Volume 11297, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

The development of optical modes with intrinsic structure has significantly redirected attention to the established concept and fundamental physics of the photon. In particular, to accommodate the modal structure of beams with transverse structure, two aspects of conventional representation invite special modification: the mathematical formulations, and figurative depictions. Reappraisals of the former highlight known deficiencies in simple plane wave mode expansions, at the price of associating the properties of individual quanta with macroscopic beam parameters wrought by the physical optics. Experimental proofs that such features do indeed reside in individual photons lead to conceptual problems, yet it is clear that alternative viewpoints engender still deeper difficulties. Such quandaries are also evident in the variety of diagrammatic representations used for structured radiation. Though such depictions cannot ever adequately represent the quantum physics, their incautious use can become seriously misleading, misrepresenting the underlying mathematics and supporting wrong conclusions. This analysis aims to expose and underscore some issues that invite closer attention.

Following Fermat's principle, it is intuitively assumed that a pulse always slows down while traveling from low index to high index materials. Here we show that structuring a wave-packet both spatially and temporally challenges this well-established intuition, unveiling anomalous refractive phenomena – group velocity of a pulse increases while traversing denser media. We present a theoretical formulation as well as an experimental demonstration of this remarkable behavior by making use of 'space-time' wave-packets – propagation-invariant pulsed beam endowed with tight correlations between spatial and temporal degrees-of-freedom. We observe the boost of group velocity at the interface of various optical materials (BK7, MgF2, and Sapphire) with air.

It is common both in the classical and quantum optics to describe the optical field as a superposition of plane waves. However, it is well known that optically active materials emit photons vastly dominantly in the electric dipole approximation. The photons emitted in the electric dipole transitions are not plane waves, but spherical photon states corresponding to eigenstates J = 1 of the total angular momentum and M = ±1 of the z component of the total angular momentum. In addition, electric dipole photons are separated from the magnetic photons by the state index η = e for electric photons in distinction to η = m for magnetic photons. In this work, we study the far-field of light that is generated when a two-dimensional matrix of atoms emits electric dipole photons and compare this far-field at large distance from the emitting matrix with a plane wave. The goal of our work is to find out if the light emitted from the electric dipole transitions carry the memory of being electric dipole photons when they are far from the emitting atoms. In particular, it is well known that a plane wave includes all angular momentum components corresponding to quantum numbers J = 1, 2, 3, …, while the far field of the emitting matrix can include only the angular momentum component J = 1. Although the two-dimensional atomic matrix used as a light source in our simulations is certainly nontrivial to fabricate, it is nevertheless fully physical and we expect that with some modifications, the conclusions from the present simulations can be generalized to atomic light sources that are more easy to realize experimentally.

Gaussian beam and higher modes can be introduced by making the position of their source complex (moving it to the complex point). This concept has lead later to the introduction of so-called complex source beams. We build here upon our previous development of complex source vortices (CSV) and introduce an analytical expansion of scalar CSVs into spherical multipoles. We extend it to the vector CSVs and study in detail cases of rather complex polarisation topologies. This expansion enables us to introduce a closed-form analytical Mie theory. We apply our developments to investigate chiral planar nanostructures and optimise their optical properties.

Spot diagrams are the intersection coordinate points in the image plane of the incoming rays from a point object. When the point object is imagined to be at infinity, the spot diagram can be considered as a representation of the point spread function (PSF) of the imaging lens. The performance of an imaging system for various applications can be analyzed with the help of the spot diagrams. In this paper, we will present our work using exact ray tracing that can be employed to compute the spot diagrams of both scalar and vector beams such as radially polarized beam, azimuthally polarized beam, etc.

Surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension by tuning the light wavelength to their size-dependent magnetic dipolar resonance.

Convection- and bubble-assisted nanoaperture-based plasmonic tweezers are presented to overcome the diffusion-limited trapping. Opto-thermally generated convection and bubble-induced flows rapidly transported particles from large spatial extent to plasmonic nanoapertures without relying on diffusion. The trapping time was reduced by more than order of magnitude. Moreover, the trapping time was brought within practical time limits at ultralow particle concentrations for which it could take several hours to trap a single particle.

We use dynamically controlled annular beam optical tweezers to orientate non-spherical swimming E.coli. Typically elliptically shaped particles in a Gaussian optical trap will align themselves with the direction of beam propagation. This orientation makes determining the dynamics of swimming particles difficult, as most optical tweezers systems are only able to capture information in the focal plane, but not the axial direction. We use simulations and experimental measurements to show that we are able to orientate motile E.coli from a vertical to horizontal position with a spatial light modulator in as little as one intermediate step without reduction in trap stiffness.

When the dimensions of particles approach the nanoscale, either in one dimension for thin films, two dimensions for nanowires or three dimensions for nanoparticles, their physical properties can diverge from those of bulk materials due to quantum effects. There are many potential applications for devices based on these materials. However, it is a challenge to manipulate nanoscale materials because of their ultra-small sizes. In this paper, optoelectronic tweezers (OET) are used to trap and manipulate micro/nanoscale metal particles. Metal particles with scales from tens of microns to several nanometres were successfully manipulated and nanoscale metal particles were assembled into tailored patterns. Due to the strong electrical forces induced by the OET device, metal nanoparticles were deposited onto the surface of the amorphous silicon. After removing the liquid from the OET device, these nanoparticles were attached firmly on the sample surface through Van der Waals forces which could lead to a method of producing solid-state electronic/optoelectronic devices.

Chiral molecules scatter circularly-polarized light at different rates according to their handedness and that of the incident photons. A right-handed molecule, for example, scatters right-handed circularly-polarized light at a different rate to lefthanded light. If the energy of the scattered photon is equal to that of the input, the chiroptical effect is known as Rayleigh optical activity, whilst if energy is imparted on to the material in the scattering process it is termed Raman optical activity (ROA). The vast majority of biomolecules are chiral, and ROA is a particularly important form of scattering as it underpins vibrational chiroptical spectroscopic techniques that are pivotal in determining their structures, conformations, and functionalities. Twisted beams of light that convey an optical orbital angular momentum (OAM) of ℓℏ per photon are also chiral, being able to twist either clockwise or anticlockwise along the direction of propagation, and this handedness is completely distinct from circular-polarization handedness. Here it is shown that a twisted beam of Laguerre-Gaussian light produces forms of Rayleigh and Raman optical activity that are sensitive to the direction that the beam twists, producing chiroptical effects dependent upon both the sign and magnitude of ℓ in both anisotropic and isotropic molecular systems. This circular-vortex differential scattering effect is seen to stem from electric-quadrupole transitions coupling to the gradient of the field. The scattered differential intensity is further developed to account for its distinct scattering angle and off-axis beam alignment dependencies, and prospective experimental scattering geometries are highlighted in which there is significant scope for enhanced optical activity signals using the OAM of twisted light.

We demonstrate both theoretically and experimentally how to generate wave states that are optimal for transferring momentum, torque, etc. on a target of arbitrary shape embedded in an arbitrary environment.

Particles held in optical tweezers are commonly thought to be at thermodynamic equilibrium with their environment. Under this assumption the elastic energy of the trap is equal to the thermal energy. As a result the variance of the particle position is completely independent of viscosity and inversely proportional to the optical power in the trap. Here we show that these conditions only hold for very high symmetry cases e.g. perfectly spherical particles in unaberrated, linearly polarized Gaussian traps. Here we show that any reduction in symmetry leads to asymmetrically coupled degrees of freedom. The associated force field is linearly non-conservative and the tweezer is no longer at equilibrium. In overdamped systems the effect is a underlying systematic bias to the Brownian motion. In underdamped systems, this systematic component can accumulate momentum, eventually destabilizing the trap. We illustrate this latter effect with reference to two systems, (i) an isotropic sphere in a circularly polarized trap, and (ii) a birefringent sphere in a linearly polarized trap. In both cases the instability can be approached either by decreasing air pressure or by increasing optical power. Close to instability, the trapped particle executes increasingly coherent motion that is highly sensitive to external perturbations. Potential applications to weak force sensing are discussed.

We show a dynamic counterpropagating optical trapping scheme based on a single low-NA objective and two right-angle prism mirrors µ-3D printed on a glass coverslip. Multiple beams are created with a Spatial Light Modulator and redirected to face each other by the mirrors. The key advantages of this approach are the simple alignment, the long working distance that allows trapping of large samples, the straightforward compatibility with other advanced microscopies and the intrinsic side-view of the trapped object. We demonstrate the viability of our approach by performing trapping and 3D manipulation of dielectric beads and cells.

Optically levitated nanoparticles in vacuum are a promising tool aiming for the extremely sensitive force measurements in reaching up to the order of zN•Hz^-1/2 and for the potential investigation in the field of quantum physics. In contrast to other mechanical oscillators, the optically trapped nanoparticle in vacuum has no clamping losses, its motion is influenced only by a laser beam and its potential profle and therefore the mechanical quality factor of such oscillator is very high. In water immersion the optical trap is almost exclusively considered as harmonic but in vacuum the optical potential anharmonicity starts to play an important role. This can be observed in power spectrum density profile where the oscillation peak is asymmetric. Here we demonstrate on the simulated trajectories of the levitated particle how the standard power spectral density method provides strongly biased values of parameters describing the optical trap and its surrounding properties.

Locally conserved quantities of the electromagnetic field in lossless chiral media are derived from Noether's theorem, including helicity, chirality, momentum, and angular momentum, as well as the separate spin and orbital components of this last quantity. We discuss sources and sinks of each in the presence of current densities within the material, and in some cases, as also generated by inhomogeneity of the medium. A previously obtained result connecting sources of helicity and energy within chiral materials is explored, revealing that association between the two quantities is not restricted to chiral media alone. Rather, it is analogous to the connection between the momentum, and the spin and orbital components of the total angular momentum. The analysis reveals a new quantity, appearing as the "orbital" counterpart of the helicity density in classical electromagnetism.

Vortices can be found in many types of fields, from fluid velocity fields to optical fields. In optical manipulation, we are interested in the optical force field arising from the interaction between the beam and the particle. There are several mechanisms that can lead to circulation of particles around an optical trap including transfer of angular momentum from the beam to the particle or oscillations due to a lack of damping in the dynamical system. Understanding of the creation and behaviour of vortices occurring in optical fields can provide means for creating interesting rotational dynamics for particles held in structured light fields. Here, we describe the mechanisms that can lead to circulation in an optical trap. In particular we describe how the force field vortices can be found in different trapping configurations and we discuss the relationship between force vortices, optical vortices and Brownian vortices.

This Conference Presentation, "Perfect vortex beams and their applications in classical and quantum information processing," was recorded at Photonics West 2020 held in San Francisco, California, United States.

Graded index (GRIN) lenses focus light through a radially symmetric refractive index profile. It is not widely appreciated that the ion-exchange process that creates the index profile also causes a radially symmetric birefringence variation. This property is usually considered a nuisance, such that manufacturing processes are optimized to keep it to a minimum. Here we show that this birefringence can be harnessed as a basis of a versatile and expandable vectorial state manipulator. Using standard GRIN lenses in cascade with other optical components, we generate various states, including full Poincaré beams that also contain orbital angular momentum. The combination of highly-symmetrical graded refractive index and corresponding birefringence – which benefit from the mature technology of the ion-exchange process – permit precise, simultaneous, phase and polarization modulation, which – when combined in a cascade structure with other elements – forms the basis for several applications. The non-pixelated nature of the birefringence of the lens, optical efficiency of the lens, and complex geometric phase inside the lens may also benefit future applications such as precision beam generation and quantum manipulation. All of these complex vectorial beam manipulations are achieved using off-the-shelf, inexpensive, passive optical components.

Measuring the phase of low power optical signals is important for space-based gravitational wave detection, geodesy measurements and free-space optical communications. Phase measurements are required in heterodyne interferometry and are commonly implemented by phasemeters based on In-phase and Quadrature demodulation or phase-locked loops. Laser frequency noise and quantum noise set competing requirements on phasemeter design. Poor optimisation of the phase measurement system can lead to a breakdown of the measurement due to cycle slipping, an ungraceful degradation of phase measurement performance. This talk will explore the fundamental limitations of weak light phase measurements, highlight design considerations for such a phase measurement system and present recent experimental results for weak light phase measurements. These findings may expand the design parameter space for future inter-satellite laser interferometry and communication instruments.

Conventional systems exploiting dynamic control of spatiotemporal beams using spatial light modulators are limited in data rate and power density. These are not the only limits, since the desired spatial control should include a continuum of Orbital Angular Momentum so that fractional and integer OAM states are possible, as well as coherent combinations to realize complex power flows for interaction science in linear and nonlinear regimes. This talk will summarize recent progress based on the spatial and dynamic control of Higher Order Bessel Gaussian Beams that can be reconfigured at unprecedented rates and applicable for high power densities. Applications will include propagation through dynamic turbulence, beam control and nonlinear interactions exploiting a continuum of OAM states. Future perspectives will also be discussed for a number of applications relevant to Maritime sensing.

Structured light can enhance the functionality of optical communication and sensing systems. Dense scattering environments such as those experienced in coastal water or foggy conditions result in degradation of structured optical fields. We present findings that indicate the preservation of phase structure of beams for Ballistic Light carrying Orbital Angular Momentum (OAM) propagated through a dense scattering over short (<3m) distance with attention of up to 20dB. We present a numerical channel modelling approach that can predict the scattering behaviour at extended distances, which indicate that there is a strong mode dependant variance in crosstalk from the interaction of beams that carry OAM with randomly displaced scattering particles. These result present an exciting possibility to use OAM modes as a long distance particulate sensor and could potentially lead to the development of novel tools for monitoring the particles in the environment.

We present the study of non-diffracting Mathieu beams, also known as Pendulum beams. In previous studies we studied pendulum beams that corresponded to stationary states of the quantum pendulum. In this work we present the results of superpositions of pendulum states with phases correlating to the time evolution of the quantum states of the pendulum. Thus, as a function of time, the quantum probability extracted from the beams mimicked the classical pendulum, liberating or rotating depending on whether the states involved in the superposition were below the potential barrier or above it. We also study the simple pendulum states for large values of the potential barrier.

The large bandwidth and high intensity of ultrafast vortex pulses, i.e. pulses with orbital angular momentum (OAM), open new prospects for applications in communication, imaging or nonlinear photonics. In previous experiments, we demonstrated the peculiar spatio-spectral behavior of pulsed polychromatic vortex beams in the vicinity of phase singularities. It was shown that the rotation of characteristic, so-called “spectral eyes” and the spectral dependent Gouy phase are closely connected. For practical applications, a controlled variation of spatio-spectral distributions is required. Here we report on our most recent studies concerning the dependence of time-integrated spectral maps on key optical parameters. It is shown that the speed of rotation of spectral eyes during the propagation is essentially determined by the angular and spectral profiles. This enables to modify the spectral rotation characteristics by applying low-dispersion, adaptive optical components. The performance of reflective liquid-crystal-on silicon spatial light modulators (LCoSSLMs) is compared to diffractive spiral gratings with variable illumination. Moreover, the generation of wavepackets with a time-dependent orbital angular momentum (self-torque) by superimposing multiple tailored vortex pulses is proposed. This allows for extending the capabilities vortex pulses by defined non-stationary spatio-spectral and topological characteristics.

We theoretically examine the transport properties of non-ideal optical fibres with high numerical aperture. Using a simple spectral method, we derive the modes in perturbed or non-ideal fibres from the numerically evaluated modes of circularly symmetric fibres. We then consider the propagation through the fibre of Gaussian spots, projected onto the distal fibre end. The incident spots are of uniform, arbitrary polarization and positioned at any point on the fibre facet. We then evaluate the effect of propagation through the fibre in terms of various indices. In particular, we consider the motion of the centre of energy, the average polarization state and the average spin and orbital angular momentum. The study includes both step index and graded index optical fibres with symmetric and chiral deformations. We observe a fundamental difference between propagation in step index and graded index optical fibres: in the latter case, the centre of energy converges to the fibre axis as the light propagated along the fibre and in the former it moves erratically about the transverse plane. In addition, we find that circular polarization states are preserved for cylindrically symmetric fibres, of arbitrarily high numerical aperture. However, this property is destroyed by relatively weak deformations of the fibre.

One important parameter in the case of translation of an optically trapped particle is the maximum achievable speed of translation in optical trapping. While the parameter is expected to have a dependence on the particle diameter and the viscosity of the medium, there will also be dependence on the laser power and step size of the moving trap. In this paper, we will experimentally investigate the maximum translation speed of a given trapped particle in a certain medium achievable in a holographic optical trap. We will implement the holographic trap using a liquid crystal spatial light modulator with a computer interface and use latex beads in water for trapping.

The need for ever-growing communications bandwidths has led to an interest in mode-division-multiplexed communications to increase the information carrying capacity of fiber-optic networks. More recently, mode-division multiplexed chip-scale photonic devices have been investigated as a means towards highly integrated photonic components and systems. To date, however, most chip-scale demonstrations have focused on fixed coupling and routing of individual waveguide modes on a chip. In this work we propose and investigate a new technique to dynamically couple and convert between different propagating waveguide modes via symmetry-breaking optomechanical near-field interactions. Silicon nitride waveguides (_tSi3N4=175 nm) with air top cladding are fabricated and enable propagation of weakly-confined modes with substantial evanescent field near the waveguide surface. Suspended silicon nitride (_tSiNx=200 nm) micro-electro-mechanical structures (MEMS) interact with the propagating mode’s evanescent field. However, the slight offset of the MEMS perturber with respect to the waveguide’s center axis leads to a symmetry breaking mode perturbation. This perturbation converts even propagating modes (e.g. TE₀) to higher-order odd modes (e.g. TE₁). We present various experimental techniques for characterizing the mode conversion including direct imaging, mode beating, and FFT spectrogram analysis. Simulation and experimental results demonstrate this new concept of using symmetry-breaking optomechanical near field interactions for mode coupling and conversion towards future mode-division multiplexing on a chip.