We propose an all-dielectric, self-confined cavity that supports a flat-band quasi-guided mode (QGM) to realize an ultracompact nanolaser. By setting a spacer layer between the grating and the waveguide layer, precise band engineering is achieved. Subsequently, introducing periodic perturbations folds the GM into the light cone, forming a flat-band QGM. Benefiting from the slow-light effect induced by the flat band and the inherently low radiation loss of the GM, both in-plane photon leakage and radiative loss are suppressed. Consequently, a cavity with a quality factor of approximately 2.4 × 10 3 is achieved within only 10 unit cells (5.7 λ). The flat-band QGM enables a single-mode C-band laser with a low threshold electric-field amplitude of 7.7 × 10 5 V/m, despite the minimal number of unit cells. Notably, the unique field distribution of the high-frequency flat-band mode also provides significant robustness against variations in grating depth. This flat-band-assisted design can be extended to other wavelength ranges, providing a path toward power-efficient, on-chip, and compact lasers.

A guided-mode resonance (GMR) grating-based dual-band graphene absorber is theoretically proposed for the shortwave infrared range. The absorber comprises two pairs of electrodes: the bottom electrode consists of a graphene layer and an intermediate metal layer that controls the electro-optic (EO) waveguide layer, while the top electrode includes an intermediate metal layer and a top indium tin oxide layer that controls the EO grating. This configuration enables two independently tunable absorption bands, corresponding to the metal-assisted GMR and surface plasmon resonance modes. The enhanced absorption results from the combined effects of both the graphene and the metal layers. Numerical simulations indicate that the two absorption bands exhibit distinct and separate electric field distributions while achieving high absorption rates above 90% during EO tuning. A linearly negative spectral shift of -1.8036 nm/V and -3.1146 nm/V is observed for the bands at shorter and longer wavelengths, respectively. By adjusting the geometric parameters of the structure, a broader spectral range encompassing two absorption bands can be realized. Due to its independent tunability and high absorption, the proposed device holds great potential for applications in detectors, sensors, and modulators.

We numerically present a method for realize giant Goos–Hänchen (GH) shifts enabled by accidental bound states in the continuum (BICs), wherein the grating height is identified as a critical tuning parameter for achieving high-Q resonances near the accidental BICs. By designing a one-dimensional grating with in-plane symmetry breaking, we induce pronounced reflection-phase dispersion under oblique incidence, leading to GH shifts enhanced to the order of 103λ. We show that this enhancement originates from the asymmetric modulation of the resonance linewidth and quality factor governed by the grating height. Quantitative analysis is provided by coupled-mode theory in conjunction with a Lorentzian response model. Multipole decomposition further reveals that the accidental BIC mode is predominantly governed by toroidal dipole excitations, accompanied by magnetic dipole and magnetic quadrupole contributions. Our results provide a viable route for achieving large GH shifts under high-reflectivity conditions and provide new design principles and tuning degrees of freedom for high-performance photonic devices and integrated metasurface-based sensing platforms.

To effectively address the passivity and field distribution limitations inherent in conventional refractive index (RI) sensors, we present an active laser sensor that employs a single-layer guided-mode resonance (GMR) grating with slant ridges, which simultaneously functions as both an optical cavity and a gain layer. Specifically, by leveraging slant ridges, a quasi-bound state in the continuum is excited, which destructively interferes with the inherent GMR mode featuring a broadband spectrum, resulting in a transmissive resonance mode. By exploiting its unique field distribution concentrated within the gap regions and aligning its resonance wavelength with the gain medium, our design achieves active, high-performance sensing. This work presents a promising approach for RI sensing in compact systems, such as the end facet of an optical fiber, demonstrating a pathway for high-precision and integrated laser sensor applications.

Refractive index sensors with a compact size are crucial for detection scenarios in confined spaces. Herein, we theoretically propose a metal-assisted finite-sized refractive index sensor based on grating-coupled surface plasmon polariton (SPP). Metal reflectors are incorporated at the edges of the grating to enhance photon absorption within the compact structure, thereby minimizing photon leakage and improving the resonance efficiency of SPP. The finite-difference time-domain method is employed to simulate the optical field distribution and sensing response of the grating-coupled SPP under transverse magnetic polarization. The results indicate that with an overall device length of only 6.2 & micro;m, the sensor achieves a bulk sensitivity of 1013.86 nm/RIU and a figure of merit (FOM) of 335.72 RIU-1. Additionally, the surface sensitivity is 102.07 nm/RIU, with a corresponding FOM of 30.74 RIU-1. The compact device is of great importance to the design of miniaturized optical sensors and integrated sensing systems.

Periodic dielectric structures, such as guided-mode resonance (GMR) gratings, typically serve as optical cavities. However, due to inherent losses, the quality (Q) factor for GMR cavities tends to be low. Here, we numerically report lasing action from a high-Q cavity in one-dimensional (1D) and two-dimensional (2D) GMR gratings featuring deep grooves. We achieve a high-Q state by adjusting the groove depth to slightly shift the resonance away from the bound states in the continuum, which possess an infinite Q factor. By further aligning the resonance wavelength with the emission band of the gain medium, a nanolaser with a low threshold is achieved. Using a four-level gain system and a finite-difference time-domain approach to simulate the active optical responses, we show that optically pumped lasing with directional beam emission is achieved in a GMR grating coated with an organic gain medium. Additionally, we present groove depth-regulated 2D GMR gratings with high Q factors that are notably polarization-independent. We find that the lasing action is slightly influenced by the polarization angle due to distinct electric field distributions, even though the Q factor remains constant. Our design for low-threshold nanolasers shows promise for various photonic applications, including sensing, optical communications, and bio-imaging.

Optical sensors are essential components in a variety of applications due to their real-time monitoring. Here, we propose a refractive index sensor that utilizes a topological guided-mode resonance (GMR) grating, which offers high sensing performance while maintaining a compact micrometer-scale footprint. The proposed structure features a topological interface formed by two GMR gratings with distinct topologies, which supports a leaky Jackiw-Rebbi (JR) state resonance. The JR state exhibits a highly localized electric field at the interface, leading to efficient refractive index sensing within a confined area. Additionally, the structure enables a controllable sensing area by incorporating a GMR grating in the critical phase, which functions as a region with zero Dirac mass. The proposed structure provides highly desirable properties for creating compact and effective sensors applicable in biomedical fields, environmental monitoring, and chemical analysis.

We numerically design a compact nanolaser based on a topological guided-mode resonance (GMR) structure. It consists of a topological junction formed by two GMR gratings, which induces a leaky Jackiw–Rebbi (JR) edge state that confines in-plane light within a small mode volume. Using the finite-difference time-domain (FDTD) method to simulate active optical responses, we show that surface-emitting lasing is achieved with a threshold of 4.5 µJ/cm 2 within a cavity length of approximately 2.0 µm. In addition, by replacing the junction with an array of equally spaced ridges in a critical phase, the edge mode transitions into a bulk mode. This modification allows for controllable cavity sizes of 4.9, 7.8, and 10.7 µm, with corresponding thresholds of 6.0, 8.4, and 9.0 µJ/cm 2 , achieved by using 5, 10, and 15 cycles of critical state grating. The topological GMR holds promise for compact coherent sources.

Optical refractive index sensors with small footprints are essential components in compact biomedical and chemical analysis, owing to their unique advantages in size and real-time detection. In this work, we propose a miniaturized refractive index sensor based on bound states in the continuum (BICs) by utilizing compound gratings combined with two silver (Ag) mirrors on both sides. By confining light within the central grating region through reflection of the two Ag mirrors, we achieve a sensitivity of 362.07 nm/RIU and a figure of merit (FOM) of 1956.18 RIU- 1, while maintaining a small horizontal dimension of 20.96 mu m. Additionally, BIC occurs when the grating height is tuned within the range of 771 nm-803 nm, resulting in a narrow linewidth that can be utilized to achieve an enhanced FOM of 8726.22 RIU- 1. Our research provides valuable insights for the development of high-performance on-chip sensors with compact footprints for future applications.

Bound states in the continuum (BICs) have been demonstrated as an effective mechanism to achieve high quality (Q)-factor cavities for nanolasers. However, the development of a compact BIC laser with a low threshold has remained elusive. Here, we numerically report lasing action from symmetry-protected BICs in a two-dimensional heterostructure, which consists of compound gratings with finite cells surrounded by orthogonal distributed Bragg reflectors (DBRs). The compound grating is used to excite quasi-BIC resonance with a high Q-factor, and DBRs enable light confinement and localized electric fields to enhance light-matter interaction. The nanolaser with a threshold of 16.8 mu J/cm(2) is achieved within a footprint as small as 3.35 x 3.35 mu m(2). By changing the phase adjusting gap or asymmetry degree, it is possible to control the lasing emission. This work reveals a new, to our knowledge, path toward compact BIC lasers with a simple scheme for applications that require a small footprint and low threshold.

In this paper, we propose a tunable dual-channel absorber based on a monolayer of graphene combined with a slanted grating. A single-channel perfect absorption of a monolayer graphene structure at 850 nm was initially achieved in a Fabry-Perot cavity resonance. The absorption rate of graphene was enhanced by nearly 24.5 times. Furthermore, the symmetry of the grating is broken to excite the quasi-bound states in the continuum (quasi-BICs) resonance mode, resulting in another absorption channel at 878.8 nm, thus achieving a perfect dual-channel absorber. The absorption half-width and absorption wavelength can be adjusted by tuning the grating thickness and the electro-optical effect of the DAST material. Furthermore, adjusting the polarization angle of the incident light enables the transition between single- and dual-channel absorbers. The proposed device has potential applications in the fields of high-performance graphene-based optoelectronic devices and optical switching systems.

Ultrahigh quality (Q) factor can be achieved by slightly breaking the symmetry of periodic structures, leading to the transition from symmetry-protected bound states in the continuum (BICs) to quasi-BICs (qBICs). However, it usually requires slight asymmetry because it follows inverse quadratic dependence on the degree of asymmetry. Herein, we numerically propose BIC resonances can be supported using an asymmetric grating consisting of two ridges with different widths in one unit cell. These BICs as a result of destructive interference between radiation channels are achieved by deliberately designing grating height or using oblique incidence in the structure with a large degree of asymmetry. In addition, by monitoring the wavelength shift of qBICs with changes in the surrounding medium, high sensing performance assisted by the BIC resonances is implemented. We achieve a sensitivity of 329 nm/RIU and an ultrahigh figure of merit (FOM) of 4.1x10(7) RIU-1 with a grating height of 798 nm for one of the qBICs. We also achieve a sensitivity of 479.6 nm/RIU and an ultrahigh FOM of 5.27x10(4) RIU-1 with an incident angle of 25.5 deg for other qBICs. We believe the structure and method for optical refractive index sensing are highly sought after in the fields of optical trapping, biological sensing, and miniaturized nanolasers. (c) 2024 Society of Photo-Optical Instrumentation Engineers (SPIE)

Asymmetric nanostructures that support quasi-bound states in the continuum (quasi-BIC) are known to exhibit an extremely sharp and sensitive optical resonance, making them attractive platforms for optical sensing applications. In this work, we numerically propose an asymmetric grating based on quasi-BIC for surface refractive index sensing with enhanced sensitivity and figure of merit. The gratings are realized by three asymmetric types: ridgeasymmetry, groove-asymmetry, and dual-asymmetry. Numerical simulations of the proposed structure were conducted by using the rigorous coupled wave approach and finite-difference time-domain method. At normal incidence, the three asymmetric gratings support a single quasi-BIC at 910.3 nm, a single quasi-BIC at 1067 nm, and double quasi-BICs at 910.4 nm and 1067.1 nm, respectively. The single quasi-BIC at 910.3 nm, achieved through ridge-asymmetry, and the quasi-BIC at 910.4 nm, achieved through dual-asymmetry, exhibit almost the same electric field distribution and high sensitivity of about 444 nm/RIU. At oblique incidence, another quasiBIC can be induced in ridge-asymmetry or groove-asymmetry types, which has the same resonance wavelength as the quasi-BIC in dual-asymmetry type. As the incident angle increases, the sensitivity of the quasi-BICs at longer wavelengths consistently increases in three types. Remarkably, as the angle approaches approximately 28 degrees , these quasi-BICs collapse into resonance-trapped BICs, leading to an extremely sharp resonance. Therefore, it is possible to achieve high resolution at this angle while maintaining high sensitivity simultaneously. Our study represents the first attempt to enhance the sensing performance of BIC sensors by using oblique incidence, which has significant implications for the design and application of such sensors.

A miniaturized optical refractive index sensor based on quasi-bound states in the continuum (quasi-BICs) is proposed in this work. By utilizing one-dimensional compound gratings with varying heights to break the symmetry of the grating, the structure supports the transition from BIC to quasi-BIC. Additionally, metallic mirrors are positioned at the edges of the grating to facilitate effective in-plane light confinement, thereby reducing light leakage and significantly enhancing peak efficiency within constrained dimensions. A comprehensive investigation was conducted to analyze the impact of metal height, edge spacing, and the number of periods on the resonance modes in finite structures, with the aim of optimizing structural parameters. An assessment of refractive index sensing performance was performed under TE and TM polarizations. The results indicate that the sensitivities for TM and TE polarizations are 427 nm/RIU and 434 nm/RIU, with a small footprint of approximately 18.51 mu m and 18.48 mu m, respectively. This study has the potential to enhance the design and application of miniaturized optical refractive index sensors. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

We present a nanoscale laser based on an asymmetric guided-mode resonance (AGMR) structure. The AGMR creates hybrid resonant modes, which consist of the newly generated quasi-bound states in the continuum (quasiBICs) and the intrinsic GMR mode. By modifying the structural parameters, the GMR and quasi-BICs modes can be matched with the pump and emission wavelengths of the gain medium, respectively. Therefore, high-intensity near fields of the GMR as the resonant optical pumping mode and high quality (Q) factor of the quasi-BICs as the resonant-emitting mode jointly contribute to the low-threshold lasing behavior. The finite-difference timedomain method is used to analyze the lasing characteristics, and a threshold of 14.2 mu J/cm2 is obtained, which is approximately ten times lower than that of a single-coupled mode laser. By adjusting the asymmetry parameters and fill factor of the grating, the threshold can be further reduced to 8.9 mu J/cm2. Additionally, we have also studied the feasibility of the AGMR structure by adjusting the simulation boundary conditions from periodic to perfectly matched layer to simulate a finite-sized structure. The findings provide a new way to excite hybrid modes, opening up possibilities for applications that demand highly confined fields and high Q-factors.

Lasers based on the resonant nanostructures have attracted much attention due to their low threshold and compact dimensions. Guided-mode resonance (GMR) structures have been studied in lasing configurations because of their optical field enhancement and convenient free space excitation. However, the GMR inherently requires a larger footprint and is not suitable for high-density packaging. Here, we present numerical evidence of a miniaturized laser implemented in a one-dimensional finite heterostructure cavity (FHC). A GMR resonator and distributed Bragg reflectors are integrated to create the FHC, which enables the efficient coupling and localization of the electric field. Numerical findings indicate that the threshold is approximately 22.5 µJ/cm2, while the emission region is confined within a length of 5.4 µm. In addition, by adjusting the coupling strength, it is capable to achieve controllable lasing emission. The proposed structure provides a compact source for high-capacity optical communications, sensing, and quantum information processing.

We propose a refractive index sensor with both high bulk sensitivity and figure of merit (FOM) that engages the guided-mode resonance (GMR) effect with the assistance of a metallic layer and structural symmetry-breaking in the grating layer. Owing to the existence of the metallic layer, the electric field at resonance can be reflected to the sensing environment, and enhanced bulk sensitivity is realized. Meanwhile, the full width at half maximum of the GMR mode can be decreased by increasing the asymmetrical degree of the grating, thus obtaining a high FOM which benefits the sensing resolution. A bulk refractive index sensitivity of 1076.7 nm/RIU and an FOM up to 35889 RIU -1 are achieved simultaneously. Other structural parameters such as the refractive index and fill factor of the grating are systematically discussed to optimize the sensing performance. The proposed GMR sensor with both high bulk sensitivity and FOM value has potential uses in applications with more stringent sensing requirements.

Nanolasers based on quasi-bound states in the continuum (quasi-BIC) have attracted much attention owing to their unique optical properties providing strong light-matter interaction. Although various quasi-BIC lasers have been designed, so far, few efforts have been devoted to their tunability in wavelength. Here we propose an approach to employ quasi-BIC and guided mode in a slanted resonant waveguide grating. The proposed structure supports a specially designed eigenmode localized both in the grating and in the 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) layer, which allows it to obtain lasing emission as well as the ability to tune the wavelength. Numerical simulation results show that the threshold is approximately 7.75 μJ/cm2 with the tuning range being 28 nm. In addition, we show that the distribution of the lasing intensity between the transmission and reflection directions can be controlled by changing the parameters of the structure. This work shows good potential of combining quasi-BIC with guided mode to design tunable nanolaser.

The attribute of bound states in the continuum (BICs) for highly efficient flat-top filter by using a slantedguided-mode resonance (GMR) grating is developed in this work. By introducing a slanted angle & x1d703;& xdf03;, the fullysymmetric grating is broken to transform the dark BICs into bright quasi-BICs mode. Theoretical analysis basedon the finite-different time-domain method is applied to evaluate the filtering performances. It is found that theGMR and quasi-BICs peaks combine at & x1d703;& xdf03;= 31.4 degrees, and the flat-top filtering response is realized at the centralwavelength of 1550 nm under normal incidence. Moreover, the linewidth-tunable and central wavelength-tunable spectral response can be varied according to the change in the coupling strength of the GMR gratingby changing the structural parameters such as period, fill factor and refractive index of the grating. It is the firstreport of a flat-top filter designed by combining GMR and quasi-BICs. The proposed structure shows promisefor application in high-performance optical communication systems

A new type of dye laser is proposed based on a guided-mode resonance (GMR) transmission structure using coupled gratings. By distributing the laser dye in the coupled gratings, controllable transmission lasing behavior was simulated. The structure excites the transmission GMR effect and causes a strong local electric field in the coupled gratings, inducing the slow light effect, which in turn enhances the interaction between light and matter. The proposed GMR structure guides laser emission in the transmission direction. Two structures with resonant wavelengths of 820 nm and 870 nm were designed and compared. A higher laser intensity can be obtained in the structure with resonance at 870 nm and a corresponding threshold and half-height width of 1.24 x 10(7) V/m and 0.8 nm, respectively. In addition, the lasing wavelength can be tuned by changing the relative position of the coupled gratings. The proposed structure is desirable for the construction of other light-emitting devices.