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Optics (physics.optics)

Wed, 19 Apr 2023

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1.Optomechanically induced optical trapping system based on photonic crystal cavities

Authors:Manuel Monterrosas-Romero, Seyed K. Alavi, Ester M. Koistinen, Sungkun Hong

Abstract: Optical trapping has proven to be a valuable experimental technique for precisely controlling small dielectric objects. However, due to their very nature, conventional optical traps are diffraction limited and require high intensities to confine the dielectric objects. In this work, we propose a novel optical trap based on dielectric photonic crystal nanobeam cavities, which overcomes the limitations of conventional optical traps by significant factors. This is achieved by exploiting an optomechanically induced backaction mechanism between a dielectric nanoparticle and the cavities. We perform numerical simulations to show that our trap can fully levitate a submicron-scale dielectric particle with a trap width as narrow as 56 nm. It allows for achieving a high trap stiffness, therefore, a high Q-frequency product for the particle's motion while reducing the optical absorption by a factor of 43 compared to the cases for conventional optical tweezers. Moreover, we show that multiple laser tones can be used further to create a complex, dynamic potential landscape with feature sizes well below the diffraction limit. The presented optical trapping system offers new opportunities for precision sensing and fundamental quantum experiments based on levitated particles.

2.Hybrid plasmonic modes for enhanced refractive index sensing

Authors:Bereket Dalga Dana, Ji Boyu, Jingquan Lin, Longnan Li, Alemayehu Nana Koya, Wei Li

Abstract: Compared to single nanoparticles, strongly coupled plasmonic nanoparticles provide attractive advantages owing to their ability to exhibit multiple resonances with unique spectral features and higher local field intensity. These enhanced plasmonic properties of coupled metal nanoparticles have been used for various applications including realization of strong light-matter interaction, photocatalysis, and sensing applications. In this article, we review the basic physics of hybrid plasmonic modes in coupled metallic nanodimers and assess their potentials for refractive index sensing. In particular, we overview various modes of hybrid plasmons including bonding and antibonding modes in symmetric nanodimers, Fano resonances in asymmetric nanodimers, charge transfer plasmons in linked nanoparticle dimers, hybrid plasmon modes in nanoshells, and gap modes in particle-on-mirror configurations. Beyond the dimeric nanosystems, we also showcase the potentials of hybrid plasmonic modes in periodic nanoparticle arrays for sensing applications. Finally, based on the critical assessment of the recent researches on coupled plasmonic modes, the outlook on the future prospects of hybrid plasmon based refractometric sensing are discussed We believe that, given their tunable resonances and ultranarrow spectral signatures, coupled metal nanoparticles are expected to play key roles in developing precise plasmonic nanodevices with extreme sensitivity.

3.Defect in Photonic Time Crystals

Authors:Snehashis Sadhukhan, Somnath Ghosh

Abstract: Photonic Time Crystals (PTCs) provide a completely new platform exhibiting light wave amplification owing to periodically varying electromagnetic properties. The need to control this amplification is becoming increasingly important, especially with the emergence of meta surface based practical realization of PTCs. The work introduces isolated temporal defect in PTCs to establish a new degree of control over the amplification. We find that in presence of the defect, the transmittance and reflectance become close to unity for a specific value of momentum (k_d) within the bandgaps accompanied by a significant impact on the amount of amplification. We show the impact of the temporal defect on the exponential growth of intensity with PTC periods. The effect primarily depends on the Floquet frequency of the PTC that becomes real at k_d giving rise to four pulses instead of two as an outcome of gap propagation. We further demonstrate that by manipulating the temporal and dielectric properties of the defect, the defect state in momentum can be tuned to serve the design interest for specialty applications.

4.On lines of constant polarisation in structured light beams

Authors:Stephen M. Barnett, Fiona C. Speirits, Joerg B. Goette

Abstract: We show that Skyrmion field lines, constructed from the local Stokes parameters, trace out lines of constant optical polarisation.

5.Temporal cavity soliton interaction in passively mode-locked semiconductor lasers

Authors:Andrei G. Vladimirov

Abstract: Weak interaction of temporal cavity solitons due to gain saturation and recovery in a delay differential model of a long cavity semiconductor laser is studied numerically and analytically using an asymptotic approach. It is shown that in addition to the usual soliton repulsion leading to a harmonic mode-locking regimes a soliton attraction is also possible in a laser with nonzero linewidth enhancement factor. It is shown numerically that this attraction can lead either to a pulse merging or to a pulse bound state formation.

6.Self-Repolarization process in dual-Omnipolarizers

Authors:Nicolas Berti, Massimiliano Guasoni, Julien Fatome

Abstract: We report on an extension of the concept of nonlinear self-repolarization process by means of two different architectures based on dual-Omnipolarizers. More specifically, we compare the performance in terms of polarization attraction capabilities provided by two novel arrangements: The first configuration relies on two cascaded Omnipolarizers, whilst the second architecture integrates an additional device directly into the feedback loop. Our study reveals that for a constant power budget, the cascading of two subsequent Omnipolarizers enables to improve the efficiency of the attraction process, yielding an output Degree-of-Polarization close to unity, but at the cost of twofold equipments.

7.Passive superresolution imaging of incoherent objects

Authors:Jernej Frank, Alexander Duplinskiy, Kaden Bearne, A. I. Lvovsky

Abstract: We investigate Hermite Gaussian Imaging (HGI) -- a novel passive super-resolution technique -- for complex 2D incoherent objects in the sub-Rayleigh regime. The method consists of measuring the field's spatial mode components in the image plane in the overcomplete basis of Hermite-Gaussian modes and their superpositions and subsequently using a deep neural network to reconstruct the object from these measurements. We show a three-fold resolution improvement over direct imaging. Our HGI reconstruction retains its superiority even if the same neural network is applied to improve the resolution of direct imaging. This superiority is also preserved in the presence of shot noise. Our findings are the first step towards passive super-resolution imaging protocols in fluorescent microscopy and astronomy.

8.Electrically-Controlled Suppression of Rayleigh Backscattering in an Integrated Photonic Circuit

Authors:Ogulcan E. Orsel, Jiho Noh, Gaurav Bahl

Abstract: Undesirable light scattering is an important fundamental cause for photon loss in nanophotonics. Rayleigh backscattering can be particularly difficult to avoid in wave-guiding systems and arises from both material defects and geometric defects at the subwavelength scale. It has been previously shown that systems with broken time-reversal symmetry (TRS) can naturally suppress detrimental Rayleigh backscattering, but these approaches have never been demonstrated in integrated photonics or through practical TRS-breaking techniques. In this work, we show that it is possible to suppress disorder-induced Rayleigh backscattering in integrated photonics via electrical excitation, even when defects are clearly present. Our experiment is performed in a lithium niobate on insulator (LNOI) integrated ring resonator at telecom wavelength, in which TRS is strongly broken through an acousto-optic interaction that is induced via radiofrequency input. We present evidence that Rayleigh backscattering in the resonator is almost completely suppressed by measuring both the optical density of states and through direct measurements of the back-scattered light. We additionally provide an intuitive argument to show that, in an appropriate frame of reference, the suppression of backscattering can be readily understood as a form of topological protection.