The introduction of higher-order topological insulators featuring topological corner states has been an extremely active topic for the generation of confined modes. Recent studies show that corner states are not an exclusive feature of topological insulators but can also exist as bound states in the continuum (BIC). This suggests that corner states may exist in different topological phases that exhibit a higher-order character, beyond the conventional bulk-edge correspondence. In this paper, we show that corner states can appear in a higher-order Dirac semimetal phase of a two-dimensional photonic lattice. Such a lattice displays a dispersion relationship with a fourfold degeneracy, which serves to induce a higher-order topological phase transition, leaving a Dirac point between two edge bands. Just as Dirac modes exist in regular lattice defects, the nonconventional bulk-edge-corner correspondence leads to corner states in the Dirac semimetal phase. Notably, the induced corner state exhibits an algebraic decay characteristic of long-range interactions, predicted by the massless Dirac equation. The analysis of the field profile and quality factors indicates that the state is not a BIC, but rather a corner-Dirac state. We show that if the photonic lattice does not present a higher-order phase transition the existence of the corner-Dirac state does not arise. The results obtained in this paper indicate that corner states can exist throughout the entire topological phase transition process, even in the semimetal phase, and pave the way to generate light-matter interactions with such a photonic bath.

Topological photonics has established itself as a promising area for the development of photonic integrated circuits due to the robust properties of topological states. In recent years, different logical devices have been proposed to form the fundamental elements of an integrated topological photonic circuit. Despite the rapid theoretical growth of topological photonics, it still lacks experimental foundations concerning logical devices for on-chip integration. For this reason, in this work, we report the design and build of an all-optical photonic switch in a silicon slab working under the higher-order topological spin Hall effect. We have taken advantage of the gapped edge states due to the higher-order topology and combined this feature with changes in the dielectric permittivity of silicon by inducing transitions of free charge carriers. The transitions of charge carriers were realized through the incidence of electromagnetic radiation with a frequency close to the visible-ultraviolet region boundary, making the device operation entirely optical. The behavior of the constructed device has also been numerically simulated and compared with the experimental results obtained. This work contributes to the idea that photonic crystals are a powerful platform for studying topological states and paves the way for the experimental realization of integrated topological optical circuits.

In this work, we study a composite zinc oxide photonic crystal (PhC) that includes a meso-cavity coupled to a PhC L3 microcavity to obtain a double resonance effect and second-harmonic generation (SHG) conversion efficiency as high as 468 W ⁻¹ . This exceptional conversion efficiency was attributed to the high quality-factors Q found in the fundamental and second-harmonic (SH) modes whose values were of the order of 10 ⁵ and 10 ⁶ , respectively. Since the L3 microcavity plays a relevant role in the SHG of the composite PhC, we performed a calculation of its photonic band structure to observe the induced modes in its bandgap. Furthermore, we also found that the resonant mode adjusted to the frequency of the SH exhibits high Purcell factors of the order of 10 ⁵ . Hence, in a semiconductor material, it can be easily enhanced the light emission at the SH frequency using an adequate driving fundamental frequency light beam. These results can stimulate the engineering of photonic nanostructures in semiconductor materials to achieve highly efficient non-linear effects with applications in cavity quantum electrodynamics.

This work presents an exhaustive visualization of the airflow expulsed by a person while breathing, talking, exhaling, and blowing inside a closed room wearing a disposable face mask like those used in hospitals for patient protection and those who care for them. An optical schlieren experimental arrangement was used to obtain some of the relevant physical characteristics of the airflow, such as its refractive index gradient, the distribution of temperature, and the associated velocity field for all the tests developed. We tested three face masks, one of the surgical types and the others of the N95 series with denominations KN95 and 3MN95 (Aura TC-84A-8590). The results show appreciable differences between the masks evaluated; the surgical mask was the one that allowed the most abrupt output airflow through it in the field of view of the experimental setup. However, were also found some differences in the performance of the KN95 and 3MN95 masks. The KN95 face mask had the best performance since it expulsed to its surroundings the lowest airflow with different physical properties to the input airflow. The results obtained are relevant since it was possible to estimate the expulsed airflow velocity as a function of the distance for every face mask tested, which allows for understanding its filtering capacity by restricting the flow of potential pathogens from the mouth or nose of one person to another. Undoubtedly, the airflow behavior determination around a face mask can help to reduce the risk of spreading infectious airborne particles.

In this work, we performed a study of an interferometric high sensitivity photonic crystal (PhC) sensor applied to measure glucose concentration in human urine samples. The architecture of the photonic sensor numerically simulated is based on a Mach–Zehnder interferometer formed by a coupled waveguide-cavity system. The sensor operates using photonic mode transitions detected from the photonic band diagram analysis, driven by changes in the glucose concentration in the urine samples that affect the refractive index of the optical sampling cavity. The photonic mode transition causes a phase shift between the wave traveling in the reference arm of the interferometer and the propagating electromagnetic wave in the sensing cavity containing the probing sample. As a consequence, the transmittance at the output of the interferometer can be modulated, making it extremely sensitive to changes in the refractive index of the sensing cavity. Since the PhC sensor studied works under variations in transmittance, we proposed a sensitivity coefficient as a function of the change in transmittance per unit change in the refractive index. The sensitivity achieved by the photonic sensor presents a value of 7000%/RIU, which indicates a variation in transmittance of 70% for changes in the refractive index of 0.01. These results demonstrate the feasibility of using photonic transitions between modes as a sensing tool in integrated photonic devices.

Small-scale and supersonic convergent-divergent type micro-nozzles with characteristic sizes of around a few centimeters and exit and throat radii of tenths of millimeters were the subjects of this study. Using the schlieren Z-type optical technique, the supersonic airflows established at the exit of seven nozzles were visualized. The dependence of the shock cell characteristics on the nozzle pressure ratio (NPR), defined as the ratio of stagnation pressure to atmospheric pressure, was analyzed. The dependence of the nozzle thrust and the specific impulse on the NPR ratio and the mass flow rate was also studied using a simple device based on concepts of fluid mechanics. The results obtained are in agreement with similar results obtained in recently published research on double-bell nozzles. The thrust of all nozzles depends linearly on the shock-cell spacing, which is one of the most relevant findings of this research. In other words, the output airflow structure determines the performance of the nozzles, such as the thrust or the specific impulse they produce. These small nozzles offer significant advantages over conventional nozzles in low energy consumption and lower manufacturing cost, making them suitable for scientific research in space micro-propulsion and cooling microelectronic systems, among other applications.