András Szenes

Plasmonic Structure Integrated Single-Photon Detector Configurations to Improve Absorptance and Polarization Contrast

Configurations capable of maximizing both the absorption component of system detection efficiency and the achievable polarization contrast were determined for 1550 nm polarized light illumination of different plasmonic structure integrated superconducting nanowire single-photon detectors (SNSPDs) consisting of p = 264 nm and P = 792 nm periodic niobium nitride (NbN) patterns on silica substrate. Global effective NbN absorptance maxima appear in case of p/s-polarized light illumination in S/P-orientation (γ = 90°/0° azimuthal angle) and the highest polarization contrast is attained in S-orientation of all devices. Common nanophotonical origin of absorptance enhancement is collective resonance on nanocavity gratings with different profiles, which is promoted by coupling between localized modes in quarter-wavelength metal-insulator-metal nanocavities and laterally synchronized Brewster-Zenneck-type surface waves in integrated SNSPDs possessing a three-quarter-wavelength-scaled periodicity. The spectral sensitivity and dispersion characteristics reveal that device design specific optimal configurations exist.

Enhancing diamond color center fluorescence via optimized plasmonic nanorod configuration

A novel numerical methodology has been developed, which makes possible to optimize arbitrary emitting dipole and plasmonic nano-resonator configuration with an arbitrary objective function. By selecting quantum efficiency as the objective function that has to be maximized at preselected Purcell factor criteria, optimization of plasmonic nanorod-based configurations has been realized to enhance fluorescence of NV and SiV color centers in diamond. Gold and silver nanorod-based configurations have been optimized to enhance excitation and emission separately, as well as both processes simultaneously, and the underlying nanophotonical phenomena have been inspected comparatively. It has been shown that considerable excitation enhancement is achieved by silver nanorods, while nanorods made of both metals are appropriate to enhance emission. More significant improvement can be achieved via silver nanorods at both wavelengths of both color centers. It has been proven that theoretical limits originating from metal dielectric properties can be approached by simultaneous optimization, which results in configurations determined by preferences corresponding to the emission. Larger emission enhancement is achieved via both metals in case of SiV center compared to the NV center. Gold and silver nanorod-based configurations making possible to improve SiV centers quantum efficiency by factors of 1.18 and 5.25 are proposed, which have potential applications in quantum information processing.

Plasmonic Structure Integrated Single-Photon Detectors Optimized to Maximize Polarization Contrast

Numerical optimization was performed via COMSOL multiphysics to maximize the polarization contrast of superconducting nanowire single photon detectors (SNSPDs). SNSPDs were integrated with four different types of 1D periodic plasmonic structures capable of mediating p-polarized photon selectivity to the niobium-nitride superconducting nanowire pattern. Optimization with two different criteria regarding the maximal tilting resulted in wavelength-scaled periodic integrated structures, which have different geometrical parameters, and exhibit different polar angle dependent optical responses and dispersion characteristics, as well as accompanying near-field phenomena at the extrema. Polarization contrast of 6.4·10² and 3.3·10²/6.9·10¹¹ and 1.4·10¹¹/1.8·10¹³ and 7.9·10¹²/1.9·10 ³ and 1.2·10⁵ can be achieved in nanocavity-/nanocavity-deflector-/nanocavity-double-deflector-/nanocavity-trench-array-integrated P-SNSPDs optimized with 85° and 80° criterion, regarding the maximal tilting.

Improved emission of SiV diamond color centers embedded into concave plasmonic core-shell nanoresonators

Configuration of three different concave silver core-shell nanoresonators was numerically optimized to enhance the excitation and emission of embedded silicon vacancy (SiV) diamond color centers simultaneously. Conditional optimization was performed to ensure ~20–30–40 and 50% apparent quantum efficiency (cQE) of SiV color centers. The enhancement spectra, as well as the near-field and charge distribution were inspected to uncover the underlying nanophotonical phenomena. The conditionally optimized coupled systems were qualified by the product of the radiative rate enhancements at the excitation and emission, which is nominated as Px factor. The optimized spherical core-shell nanoresonator containing a centralized emitter is capable of enhancing the emission considerably via bonding dipolar resonance. The Px factor is 529-fold with 49.7% cQE at the emission. Decentralization of the emitter leads to appearance of higher order nonradiative multipolar modes. Transversal and longitudinal dipolar resonance of the optimized ellipsoidal core-shell resonator was tuned to the excitation and emission, which results in 6.2∙105Px factor with 50.6% cQE at the emission. Rod-shaped concave core-shell nanoresonators exploit similar transversal and longitudinal dipolar resonance, moreover they enhance the fluorescence more significantly due to their antenna-like geometry. Px factor indicating 8.34∙105 enhancement is achievable while the cQE is 50.3% at the emission.

Optimized Superconducting Nanowire Single Photon Detectors to Maximize Absorptance

Dispersion characteristics of four types of superconducting nanowire single photon de- tectors, nano-cavity-array-(NCA-), nano-cavity-deflector-array-(NCDA-), nano-cavity-double-deflector- array-(NCDDA-) and nano-cavity-trench-array-(NCTA-) integrated (A-SNSPD) devices were optimized in three periodicity intervals commensurate with half-, three-quarter- and one surface plasmon polariton wavelength. The optimal configurations capable of maximizing absorptance in niobium nitride corre- spond to periodicity-dependent tilting in S-orientation (90 ◦ azimuthal orientation). In NCAI-A-SNSPDs absorptance maxima are reached at the plasmonic Brewster angle due to light tunneling. The absorp- tance maximum is attained in a wide plasmonic-pass-band in NCDAI1/2∗λ-A, inside a flat-plasmonic- pass-band in NCDAI3/4∗λ-A and inside a narrower plasmonic-band in NCDAIλ-A. In NCDDAI1/2∗λ- A bands of strongly-coupled cavity and propagating plasmonic modes cross, in NCDDAI3/4∗λ-A an inverted-plasmonic-band-gap develops, while in NCDDAIλ-A a narrow plasmonic-pass-band appears inside an inverted-minigap. The absorptance maximum is achieved in NCTAI1/2∗λ-A inside a plasmonic- pass-band, in NCTAI3/4∗λ-A at an inverted-plasmonic-band-gap center, while in NCTAIλ-A inside an inverted-minigap. The highest 95.05% absorptance is attained at perpendicular incidence onto NCTAIλ- A. Quarter-wavelength type cavity modes contribute to the near-field enhancement around NbN seg- ments except in NCDAIλ-A and NCDDAI3/4∗λ-A. The polarization contrast is moderate in NCAI-A- SNSPDs (∼ 10 2 ). NCDAI- and NCDDAI-A-SNSPDs make possible to attain considerably large polar- ization contrast (∼ 10 2 − 10 3 and ∼ 10 3 − 10 4 ), while NCTAI-A-SNSPDs exhibit a weak polarization selectivity (∼ 10 − 10 2 ).

Enhancing Diamond Fluorescence via Optimized Nanorod Dimer Configurations

Light extraction from silicon (SiV) and nitrogen (NV) vacancy diamond color centers coupled to plasmonic silver and gold nanorod dimers was numerically improved. Numerical optimization of the coupled dipolar emitter—plasmonic nanorod dimer configurations was realized to attain the highest possible fluorescence enhancement by simultaneously improving the color centers excitation and emission through antenna resonances. Conditional optimization was performed by setting a criterion regarding the minimum quantum efficiency of the coupled system (cQE) to minimize losses. By comparing restricted symmetric and allowed asymmetric dimers, the advantages of larger degrees of freedom achievable in asymmetric configurations was proven. The highest 2.59 × 108 fluorescence enhancement was achieved with 46.08% cQE via NV color center coupled to an asymmetric silver dimer. This is 3.17-times larger than the 8.19 × 107 enhancement in corresponding symmetric silver dimer configuration, which has larger 68.52% cQE. Among coupled SiV color centers the highest 1.04 × 108 fluorescence enhancement was achieved via asymmetric silver dimer with 37.83% cQE. This is 1.06-times larger than the 9.83 × 107 enhancement in corresponding symmetric silver dimer configuration, which has larger 57.46% cQE. Among gold nanorod coupled configurations the highest fluorescence enhancement of 4.75 × 104 was shown for SiV color center coupled to an asymmetric dimer with 21.8% cQE. The attained enhancement is 8.48- (92.42-) times larger than the 5.6 × 103 (5.14 × 102) fluorescence enhancement achievable via symmetric (asymmetric) gold nanorod dimer coupled to SiV (NV) color center, which is accompanied by 16.01% (7.66%) cQE.

Optimization of plasmonic structure integrated single-photon detector designs to enhance absorptance

Plasmonic structure integrated SNSPD configurations were optimized for 1550 nm p-polarized light illumination to maximize absorptance. Orientation dependent NbN absorptance, spectral sensitivity and dispersion characteristics were investigated.

Plasmon enhanced single-photon detection

Novel infrared superconducting nanowire single-photon detectors (SNSPD) were designed, which comprise a meandered pattern of niobium-nitride (NbN) stripes and different integrated plasmonic structures on silica substrate. To enhance absorptance of 1550 nm wavelength p-polarized light, patterns with p=264 nm periodicity were investigated, while to enhance detection efficiency, patterns with P=792.5 nm periodicity commensurate with the wavelength of surface plasmon polaritons at silica-gold interface were also designed. In OC-SNSPDs integrated with ~quarter-photonicwavelength nano-optical cavity closed by a gold reflector, the highest 63/27 % absorptance was attained in p/P-pitch design at perpendicular incidence onto NbN patterns in P-orientation corresponding to incidence plane parallel to the stripes, due to the E-field antinode at the NbN-silica interface. In NCAI-SNSPDs, where each NbN stripe is located at the entrance of a quarter-plasmon-wavelength MIM nano-cavity, enhanced 85.1/34 % absorptance is attainable in p/Ppitch design at perpendicular incidence in S-orientation, when the incidence plane is perpendicular to the integrated pattern, due to collective resonances. The maximal 95.3/70.3 % absorptances are attained at large tilting corresponding to plasmonic Brewster angles via ultra-broadband tunneling. In NCDAI-SNSPDs the longer vertical gold segments with P-pitch, which can be embedded into the silica substrate via two-step lithography, enable to attain large absorptance at small polar angles in S-orientation, due to efficient grating-coupling phenomenon. The highest 92.7/75 % absorptances are attained at 19.85°/19.35° polar angles in p/P-pitch design. P-pitch NCDAI-SNSPD supporting coupled surface waves capable of ensuring synchronous E-field enhancement below the NbN stripes is proposed for detection efficiency maximization in specific spectral-bands.