and plasmonic nanolasers, [8][9][10] have been proposed. In the development of plasmonic devices, as the structural size shrinks and the plasmonic effect increases, competition between the enhancement of light-matter interaction and increased internal loss inevitably arises and must be prioritized in the design process, as it strongly affects lasing performance. Therefore, a scaling law for plasmonic cavities is urgently needed and must be integrated into the development of any type of plasmonic nanolaser. In 2017, Wang et al. demonstrated an unusual scaling law for nanosquare plasmonic nanolasers. [11] The lasing mechanism is affected by whispering gallery mode (WGM) resonance, and a scaling law that accounts for WGM resonance can be determined from two geometric parameters: the width and thickness of the CdSe nanosquare. When these two parameters approach the optical diffraction limit, the observed difference in the lasing threshold or power consumption between plasmonic and photonic lasers dramatically increases. Plasmonic lasers generally exhibit a lower lasing threshold than photonic lasers, which implies that plasmonenhanced light-matter interaction dominates the entire laser operation. Consequently, a suitable size for plasmonic lasers can be obtained.Because the scale of plasmonic devices is equal to or below the optical diffraction limit, determining the lasing mode and observing the near-field is difficult, which may lead to inaccurate estimations in the optical design process and calculation of the scaling law. A rigorous method for identifying the plasmonic or photonic mode resonating in the cavity is thus crucial. In 2014, Sun et al. used a modified Young's inter ference method to determine the order of photonic Fabry−Pérot modes in a wire structure. [12] The angle-resolved photoluminescence (ARPL) signals of a CdS-nanostructure laser reveal a clear relation between mode parity and lasing peaks. According to the phase correlation of various longitudinal modes, the operation mode in the laser cavity can be identified. Moreover, some studies used the ARPL spectra to resolve the near-field oscillation and distinguish the photonic Fabry−Pérot mode and WGM mode in the perovskite microplate. [13] The direction of inter ference fringes shown in the ARPL spectra is related to the oscillation direction of the lasing mode, which is beneficial to identify different longitudinal modes in the laser cavity. Additionally, the far-field polarization can be further applied to Surface plasmons exhibit an extraordinary capability to reduce the structural size and improve light−matter interaction. However, for small-sized plasmonic cavities, the optical diffraction limit makes the near-field difficult to observe, complicating the analysis of exact lasing characteristics. In this study, a 4f measurement system is used to extract the mode parity from the interference pattern and reconstruct the near-field of the hybrid plasmonic perovskite nanolasers. In conjunction with other measurements, a series of rigorous methods fo...

We propose a straightforward and effective approach to design, by pattern-tunable strain-engineering, photonic topological insulators supporting high quality factors edge states. Chiral strain-engineering creates opposite synthetic gauge fields in two domains resulting in Landau levels with the same energy spacing but different topological numbers. The boundary of the two topological domains hosts robust time-reversal and spin-momentum-locked edge states, exhibiting high quality factors due to continuous strain modulation. By shaping the synthetic gauge field, we obtain remarkable field confinement and tunability, with the strain strongly affecting the degree of localization of the edge states. Notably, the two-domain design stabilizes the strain-induced topological edge state. The large potential bandwidth of the strain-engineering and the opportunity to induce the mechanical stress at the fabrication stage enables large scalability for many potential applications in photonics, such as tunable microcavities, new lasers, and information processing devices, including the quantum regime.

We realized off-Γ lasing using the Friedrich-Wintgen bound state in the continuum (FW-BIC) in a one-dimensional suspended high-contrast grating (HCG). A clear anticrossing was observed in the band diagram of the HCG corresponding to the coupling between the specific different orders of Bloch modes, and the FW-BIC with a high quality factor and large confinement factor was observed near the anticrossing point. Owing to these outstanding characteristics, the FW-BIC can serve as a robust and extraordinary cavity mode for realizing low-threshold laser operation and for achieving angle-steering laser beams. The conditions of the FW-BIC can be modulated by tuning the geometry related to the coupling modes in the anticrossing, resulting in a tunable lasing direction observed in the measurement. Furthermore, through appropriate design, the emission angle can be controlled precisely within a wide tunable range. Therefore, FW-BICs can be used to realize high-resolution directional lasing within a wide range of emission angles; they can also be applied in three-dimensional sensing for lidar applications.

Surface plasmons have robust and strong confinement to the light field which is beneficial for the light−matter interaction. Surface plasmon amplification by stimulated emission of radiation (SPACER) has the potential to be integrated on the semiconductor chip as a compact coherent light source, which can play an important role in further extension of Moore's law. In this study, we demonstrate the localized surface plasmon lasing at room temperature in the communication band using metallic nanoholes as the plasmonic nanocavity and InP nanowires as the gain medium. Optimizing laser performance has been demonstrated by coupling between two metallic nanoholes which adds another degree of freedom for manipulating the lasing properties. Our plasmonic nanolasers exhibit lower power consumption, smaller mode volumes, and higher spontaneous emission coupling factors due to enhanced light−matter interactions, which are very promising in the applications of high-density sensing and photonic integrated circuits.

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