We study the coherent interaction between a hybrid nanostructure and a strong pump electromagnetic field as well as a weak electromagnetic probe field, focusing on how various parameters influence the line shape of the four-wave-mixing (FWM) spectrum. More specifically, we examine the dependence of the FWM spectrum exhibited by a semiconductor quantum dot that is coupled with an ellipsoidal metal nanospheroid (MNS) on the interparticle distance and the depolarization factor. First, we derive the differential equations that determine the evolution of the density matrix elements in the rotating wave and dipole approximations and expand the density matrix elements, to first order with respect to the weak probe field. We then solve the equations of the density matrix, in steady state, and calculate the FWM spectrum. The investigation of the impact of the interparticle distance and the depolarization factor on the position and the width of the resonance follows. The derivation of analytical solutions of specific density matrix elements enables us to calculate the effective Rabi frequency that is introduced in the dressed-state description to predict the position of the effective resonances appearing in light-matter interaction. We demonstrate that the spectral line shape shifts from triple-peaked to single-peaked, while its amplitude is significantly suppressed, when the interparticle distance drops below a critical value that depends on the depolarization factor of the MNS. The highest critical distance occurs for a prolate MNS with high eccentricity, provided that the incident field's polarization direction is parallel with the nanostructure's symmetry axis, and the pump field detuning is positive and has a high absolute value. The spectral profile shows negligible dependence on the interparticle distance for an exactly resonant pump field with a polarization vector perpendicular to the MNS's polar axis, especially if the MNS is an oblate spheroid with high eccentricity.

The intrinsic non-linearity in silicon has led to this material being proven to be quite useful in the field of quantum optics. A quantum signal source in the form of single photons is an inherent requirement to the principle of quantum key distribution technology for secure communications, since a message that is encrypted via a quantum source cannot be branched or stolen. Here, we present the numerical simulations of a silicon ring with 6-micron radius side-coupled to the bus waveguide as a source for the generation of single photons by exploring the process of degenerate spontaneous four-wave mixing (SFWM). The free spectral range (FSR) is quite large, which simplifies the extraction of signal/idler pairs. The phase matching condition is considered by studying relevant parameters like dispersion and non-linearity. We optimize the ring to achieve a high quality factor by varying the gap between the bus and the ring waveguide. This is the smallest ring studied for photon pair generation, with a quality factor as high as 10⁵. The width of the waveguides is chosen so that the phase matching condition is satisfied, allowing for the propagation of fundamental modes only. The bus waveguide should be pumped at one of the ring resonances with minimum dispersion (1543.5 nm in our case) so that the principle of energy conservation is satisfied. The photon pair generation rates achieved are already better in the low-pump-power regimes in comparison to those discussed in the literature. Such miniaturized structures will prove beneficial for future on-chip architectures where multiple single photon source devices are required on the same chip.

Quantum correlations are crucial in modern quantum photonics research. The first discussions concerning quantum correlations were presented in the first half of the 20th century [1]. Nevertheless, currently, one can find many papers dealing with those topics. It is worth noting that some of these are devoted to optical and photonic models, and some concern proposals of new photonic systems.

Many papers deal with quantum correlations, especially in the context of applications of the considered quantum models in quantum information theory systems. At this point, one can mention correlations such as quantum entanglement, quantum steering, and Bell-type nonlocalities. These correlations are mostly related to spatial nonlocalities. On the other hand, one can ask about the existence of the counterparts of such nonlocalities in the time domain. The topics related to them are devoted to violating Legget–Garg inequalities (LGI) [2,3], which we consider here.

In this communication, we consider a system of two mutually coupled quantum nonlinear oscillators that are continuously driven by an external coherent field. For such a model, we discuss temporal correlations, examining LGI’s violation. We analyze various scenarios of measurements based on projection onto different Bell states, showing that the possibility of violating LGI inequalities is related to the choice of different projectors.

1. E. Schrodinger, Proc. Camb. Phil. Soc., 31:555 (1935); ibid 32, 446(1936).
2. A. J. Leggett, A. Garg, Phys. Rev. Lett. 54:857 (1985).
3. J. K. Kalaga, A. Kowalewska-Kudłaszyk, W. Leoński, J. Perina Jr., Opt. Express, 32:9946. (2024).

Since the 1970s, optical fibers have undergone considerable development and are now used in a very wide range of applications, covering telecommunications, the environment, medical applications, etc., thanks to the development of amplifiers, lasers, and sensors. Such progress has been made possible by the considerable work carried out to improve the transparency of optical fibers, i.e., by removing absorbing centers (such as iron ions) and structural and compositional heterogeneity. In contrast to this approach, a new family of optical fibers has been developed in recent years, incorporating heterogeneity, such as dielectric nanoparticles. Such fibers were first envisaged as a means of locally modifying the chemical and structural environment of luminescent ions (rare-earth and transition metal ions) in order to offer new fiber lasers and amplifiers. However, light scattering induced by the nanoparticles imposes severe drawbacks for those applications. Very recently, light scattering has been reported to be of great interest to developing sensors (temperature, stress, chemistry, biology, etc.). To exploit the light-scattering property, two main methods wereused to analyzed the sensors, based on optical backscatter reflectometry and transmission reflexion analysis. This presentation will review these fibers, presenting the fabrication processes, the fundamental issues involved in nanoparticle formation, and their different applications.

Carbon dots (CDs) have been widely studied as an alternative to quantum dots, semiconductors, and rare-earth-element-doped structures, as they are non-toxic and metal-free optical materials [1,2]. In medicine, they might be used, for example, in drug delivery, diagnostic, and sensing [3].

CDs were synthesized using low-temperature ammonium citrate pyrolysis, and their structure (XRD, TEM, FT-IR) and optical properties were analyzed. The TEM analysis showed that blue-emitting carbon dots (bCDs) have spherical shapes with a 4-7 nm diameter, and green-emitting CDs (gCDs) have the shape of rods with a length of 20-50 nm. The sol–gel method was used to synthesize silica and silica–calcia monoliths with embedded CDs. The aim of the experiment was to obtain composites in which the luminescence of the CDs could be observed and further used to monitor different biological processes. For that reason, glasses with different concentrations of CDs (0.03-0.2 wt.%) were prepared, and optical properties (absorption, excitation, and emission) were measured. It was found that the addition of urea during the synthesis of CDs led to a change in the emission color of the CDs from blue (λ_em: 450 nm) to green (λ_em: 540 nm). Comparing the emission spectra of the CDs, colloids, and composites, changes in the maximum emission and its intensity were observed. The emission intensity of CDs is lower in glass structures, and the maximum emission shows a red shift in glass composites. Spectroscopic measurements showed that the luminescence intensity and emission maximum depend on the excitation wavelength.

Acknowledgment

This work was supported by the National Centre for Research and Development research grant No. LIDER/26/0121/L-12/20/NCBR/2021

References

[1] Zhang W. et al., RSC Adv., 2017, 7, 20345-20353

[2] Qu D. et al., Scientific Reports, 2014, 4, 5294

[3] Kaurav H. et al., Frontiers in Chemistry, 2023; 11, 1227843

Introduction

We demonstrate a method for measuring the dispersion of a device under test (DUT), which utilizes light reflections at the edge and within an integrated waveguide to create a Michelson interferometer. The interference fringes of the Michelson interferometer depend on the group delay experienced in it.

Methods

In the DUT, the reflected power is recorded during a single, fast laser sweep. For an optical cavity with a free spectral range of Δf, the group delay (τ) is inversely proportional to Δf [1]. By finding the local period in the reflected spectrum, τ can be found as a function of frequency, and from this, the dispersion as the slope of τ.

Results

The DUT is a linearly chirped Bragg grating designed to generate a dispersion of -45.9 ps². We took nine different measurements of the same device. From the experimental data, τ was found to be noisy at low frequencies and only the linear portion of τ was considered. We found the dispersion to be (-45.5± 11.2) ps².

Conclusion

Our step-by-step data analysis confirms that, analyzing interferometric fringes from DUT light reflections offers a fast method for measuring photonic iIntegrated circuit dispersion, which aligns well with design values. This approach could serve as an alternative to established methods [2], which we will further verify in the future.

References:

1. Schwelb, J. Light. Technol. 22, 1380 (2004). Journal of Lightwave Technology.
2. Costa, IEEE Trans. on Microw. Theory Tech. 30, 1497 (1982)

Transparent glass ceramics activated with rare earth ions are valued for their excellent optical properties [1]. Silica–hafnia binary systems have emerged as an ideal matrix for integrating rare earth ions into hafnia nanocrystals, resulting in a considerable increase in luminescence and allowing for a wide variety of important applications. This work focuses on the Tb³⁺/Yb³⁺-driven down-conversion process, widely utilized in photovoltaic systems.

Following a well-consolidated protocol and an appropriate thermal treatment, the silica–hafnia glass-ceramic films were fabricated using the spin-coating technique via the sol–gel method. Interestingly, sol–gel technology offers the ability to create multicomponent materials with controlled composition, shape, morphology, and optical properties for the final product.

This investigation concentrates on silica–hafnia glass-ceramic films with a composition of 70SiO₂-30HfO₂ that have been doped with 19% rare earth ions ([Tb + Yb] / [Si + Hf] = 19%). Two primary findings are examined: (a) the temperature dependence of the intensity and broadening of the Yb³⁺ emission band at 975 nm and (b) the Tb³⁺ → Yb³⁺ energy transfer mechanism, which is based on proposed mechanisms from the existing literature. Furthermore, the power dependence of Yb³⁺ luminescence (²F_5/2 → ²F_7/2) is examined in relation to this subject [2].

In summary, these results underline the suitability of SiO₂-HfO₂ glass ceramics for photonic applications and enhance our understanding of the Tb³⁺ → Yb³⁺ down-conversion dynamics in this system.

References

[1] M.Ferrari, G.C. Righini, International Journal of Applied Glass Science, 6,240-248 (2015)

[2] Salima El Amrani, Michael Sun, Sirona Valdueza-Felip, Fernando B. Naranjo, Mohammed Reda Britel, Maurizio Ferrari, Adel Bouajaj, Effect of temperature and excitation power on down-conversion process in Tb3+/Yb3+-activated silica-hafnia glass-ceramic films,Ceramics International,2024,ISSN 0272-8842 .https://doi.org/10.1016/j.ceramint.2024.06.392.

The presented results show the synergistic effects of combining two photocatalysts (titanium oxide (TiO₂) and carbon dots (CDs)) on the enhancement of water remediation. This research involves the synthesis of fluorescent and phosphorescent carbon dots (CDs and PhCDs, respectively) and preparation of the composites, whereby they are incorporated into TiO₂ pores. Structural analysis, using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer--Emmett--Teller (BET) techniques, was conducted to assess the compositional and morphological changes resulting from CD incorporation into TiO₂.

Infrared (IR) and Raman spectroscopy allowed us to identify functional groups on the CD surface, enabling control of the optical properties of the composites. Spectroscopic studies revealed a shift in the absorption edge for the PhCDs/CDs@TiO₂ composites compared to pure TiO₂, which shows that it is possible to modulate the excitation range in the visible range. Photocatalytic activity measurements show that the PhCDs@TiO₂ composite exhibited higher activity compared to single catalysts. This enhancement is attributed to a slowdown in carrier recombination due to electron trapping in the energy band gap, leading to more efficient electron--hole separation and an increase in photocatalytic activity.

The study's results indicate that the PhCDs@TiO₂ composite has significant potential for the efficient decomposition of organic compounds in water, offering a promising solution for environmental clean-up. Additionally, the use of carbon dots opens new avenues for enhancing and modifying existing photocatalysts, paving the way for future advancements in photocatalytic applications.

Plasma Electrolytic Oxidation (PEO) is a surface treatment process that has been extensively studied in recent years for its ability to produce thick, dense metal oxide coatings. This process is especially effective on light metals, primarily enhancing their wear and corrosion resistance. Recently, the PEO process has also been used to produce composite coatings by adding luminescent nanoparticles to the electrolyte. This work presents the spectroscopic properties of PEO coatings on light metal alloys with luminescent particle additions. To increase the functionality of these coatings, various phosphors were incorporated, thereby enhancing their functional capabilities. The coatings’ structure and morphology were characterized using X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), both on the surface and in cross-section. Additionally, the chemical composition of the layers was analyzed using Glow Discharge Optical Emission Spectroscopy (GDOES) and Energy-Dispersive Spectroscopy (EDS) on both the surface and cross-sections. The photocatalytic properties of the coatings were evaluated on samples containing graphene@TiO₂ particles by monitoring the photodegradation of bisphenol A using UV-Vis absorption spectroscopy. For temperature-sensing properties, Er_0.02Yb_0.4Y_1.58O₃ additives were tested. Contactless temperature measurements were conducted across a broad temperature range to determine the most effective range for practical use. Furthermore, SiO-CaO glasses doped with Yb³⁺/Er³⁺ ions were utilized to prepare coatings on alloys that were intended for implant applications. These coatings were assessed for their ability to monitor layer bioactivity and the growth of hydroxyapatite, which is crucial for implant integration and functionality.

It was shown that the incorporation of various luminescent additives into the PEO electrolyte for coating light metal alloys enhances a surface's mechanical properties and introduces new functionalities for a wide range of optical applications.

Acknowledgements

The studies were funded from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 823942–FUNCOAT–H2020-MSCA-RISE-2018

Photonic crystals are periodic dielectric structures that exhibit photonic band gaps that strongly depend on the geometry of the lattice elements and material properties [1,2]. Since the design parameters of the photonic crystal structure are amenable to modification and adjustments, light can be manipulated and easily controlled, guided, and trapped in these structures [3]. Conventional photonic crystals have high-symmetry unit cells. Low-rotational-symmetry structures are formed by breaking the high symmetry in the photonic crystal unit cell. Low-symmetry structures are more sensitive to light manipulation and provide more control and flexibility over light with geometric and structural diversity [4]. In this study, the resonance effect in the cavity structure of a square-lattice photonic crystal composed of C2-type low-symmetry dielectric rods is investigated. The band structure, equi-frequency contours, and transmission spectra of the low-rotational-symmetry photonic crystal are obtained with Lumerical and MEEP software to examine the resonance [5,6]. Analyzing optical properties through symmetry manipulation and resonance refraction will contribute to understanding light collimation and confinement.

References:

[1] Yablonovitch E., 1993, “Photonic band-gap structures”, J. Opt. Soc. Am. B 10 283–95

[2] John S., 1987, “Strong localization of photons in certain disordered dielectric superlattices”, Phys. Rev. Lett. 58 2486–9

[3] Joannopoulos J D. et al, 2008, “Photonic Crystals: Molding the Flow of Light Second Edition (Princeton University Press)

[4] Zekeriya M Yuksel et al 2024, “Enhanced self-collimation effect by low rotational symmetry in hexagonal lattice photonic crystals”, Phys. Scr. , 99, 065017.

[5] Lumerical FDTD Solutions, Inc. http://www.lumerical.com.

[6] Oskooi, A. F. et al, 2010, “Meep: A flexible free-software package for electromagnetic simulations by the FDTD method”, Comput. Phys. Commun., vol. 181, no. 3, pp. 687–702, 2010.