Motivated by the demand for achieving high modulation depth of optical signal in three-dimensional (3D) imaging light detection and ranging (LIDAR), the electro-optic (EO) modulation depth of KTa1−x NbxO3 (KTN) crystal and its stability under the electric field have been investigated. The strong field-enhanced effect of dielectric permittivity occurs owing to the dielectric resonance, the modulation depth is enhanced, and half-wave voltage is further reduced. Only when the alternating current (AC) electric field is applied, the modulation depth increases with the increment of the electric field and trends to remain unchanged under the high owing to the saturation of polar nanoregions (PNRs) in KTN crystal. The modulation depth fluctuates with time, which can reduce the ranging accuracy of 3D imaging LIDAR. We found it can be attributed to the instability of PNRs. After applying the direct current (DC) electric field, the modulation depth was increased and its stability was enhanced owing to the improved polarization and enhanced stability of PNRs. The result reveals that the DC + AC electric field can increase the ranging accuracy of LIDAR compared to the AC electric field. We will provide guidance for designing the EO modulator in high-accuracy 3D imaging LIDAR from the perspective of nanodomain engineering and electric field-driven systems.

We present theoretical discourses, demonstrating an unusual complex light-spin conversion in a plane rectangular graphene quantum dot (RGQD), deriving at the non-perturbative intensity of the pump wave-pulse at the process of high harmonic generation. Linearly polarized excitation leads to the emission of elliptically polarized harmonics. The ellipticity and the orientation of the polarization ellipse (the tilt angle of the q’th harmonic) are derived from the Stokes parameters computed from the intensity of the different polarization components. The numerical results demonstrate that the ellipticity of the harmonics generated in RGQD can be easily tuned by changing the tilt angle of the linearly polarized pump wave pulse, without the need for complex driving systems.

Achieving asymmetric transport of photonic structures is of particular interest in many photonic applications in grating couplers and antennas for light detection and ranging. To achieve unidirectional lasing in either up-down or left-right directions, we design a one-dimensional photonic crystal slab with a parity-time symmetric configuration. Under non-Hermitian modulation and breaking of mirror symmetry, the far fields of the slab have asymmetric polarization vortex in the up-down and left-right directions, respectively, which leads to the formation of unidirectional bound states in the continuum (BIC). The plane wave incidence produces the unidirectional lasing in the up-down directions. The light incidence from the line source results in unidirectional lasing in the left–right directions. All of the unidirectional lasing is dependent on the unidirectional BIC.

A wider bio-optical waveguide is always desirable for large-field illumination of an optical waveguide microscopy. However, a wider waveguide leads to non-uniform illumination due to non-uniform evanescent field excited by multi-mode interference (MMI) patterns of waveguides. We introduce a seven-layer model of bio-waveguide for optical waveguide microscopy to analyze the waveguide-cell system. We also develop an averaging strategy of MMI pattern images by moving the coupling position to generate uniform illumination inside a wide bio-optical waveguide. Then, we systematically investigate the averaging strategy of MMI pattern images due to wide waveguide, at the wavelengths of 488, 532, and 646 nm. Finally, we demonstrate a 25% uniform improvement by the averaging strategy inside a wide bio-optical waveguide, compared with the conventional strategy.

Nanoparticle over mirror (NPoM) cavities have been a source of extreme electromagnetic field confinement in sub-nm gaps, leading to extraordinary performance for surface-enhanced Raman scattering (SERS) spectroscopy. However, the performance of the overall NPoM cavity containing a large number of nanoparticles over metal has always been a point of concern. An NPoM cavity fabricated by trapping nanoparticles with Bessel beam illumination from a fiber optic negative axicon achieved five- and two-fold enhancements for excitation wavelengths of 785 and 532 nm, respectively, while it was three- and 1.75-fold in the conventional cavity. We investigated the photodimerization mechanism of 4-aminothiophenol (4-ATP) using SERS spectroscopy within an NPoM cavity. The research is focused on the laser-induced conversion or chemical enhancement (CE) of 4-ATP to 4,4′-dimercaptoazobenzene (DMAB), a process for understanding reaction dynamics at the nanoscale. Control experiments were performed by varying excitation laser power and integration time, revealing a higher optical-driven conversion of 4-ATP to DMAB at a higher laser power. Additional control experiments focused on the impact of oxidation on the Ag film substrate. It was found that an unoxidized Ag film is ∼91% less efficient for SERS compared with an oxidized film. X-ray photoelectron spectroscopy (XPS) confirmed the presence of oxygen in oxidized film although these results provide significant insights into the reaction dynamics. The study’s limitations include trapping dependency on nanoparticle characteristics, complexity of nanoscale interactions, narrow experimental conditions, and a focus on a single reaction pathway. These factors highlight areas for future research. Ultimately, this study advances the understanding of laser-induced reactions within NPoM cavities with SERS as a powerful tool for investigating molecular transformations, suggesting potential applications in sensing and plexciton coupling.

Narrow bandpass filters (NBPFs) (an element capable of efficiently screening and transmitting optical signals in a specific wavelength range) are a key technology for modern photonic applications. However, the expansion of their stopband range and the realization of their polarization performance are still an open challenge. We proposed an optical Tamm state (OTS)-coupled metal grating narrow bandpass filter to efficiently design polarized NBPF with an ultra-wide stopband. The experimental results show that the polarization transmittance of the filter is as high as 97% in the communication band of 1.55 μm, with a Q factor of the peak being 344. The half-peak full width of the filter is 4.5 nm, and the stopband range is 1.1 to 20 μm, which is 32 times wider than that of the conventional technique. This research result not only provides a powerful method for extracting high-quality narrowband optical signals from background noise but also unfolds new possibilities for research and applications in fields such as quantum communication and optical biometrics.

We numerically study dielectric metasurface based on silicon resonators coated with polyurethane on the silicon dioxide substrate. Such metasurface can support toroidal magnetic dipole mode and quasi-bound state in the continuum (quasi-BIC) dominated by electric quadrupole with a high Q-factor by breaking the in-plane inversion symmetry. Sharply quasi-BIC with polarization-insensitive characteristics can generate strong local field enhancement distributed in the polyurethane and be used to support lasing action. Numerical results show that the pumping power threshold can be conveniently tuned by adjusting the polarization angle and can reach up to 30.2 and 51.3 μJ/cm2 in the orthogonal direction of polarization, respectively. Our findings may provide a useful guideline to design low-threshold and high-efficient miniaturized lasers.

The combined radiation power of current sources with different polarizations has been investigated through the manipulation of light propagation within zero-index materials. When the permittivity (permeability) of materials becomes zero, the amplitudes of transverse electric (magnetic) fields in media are a function of the position of the current sources. It is found that the amplitudes of electromagnetic fields excited in isotropic double-near-zero (DNZ) materials display a homogenous distribution, which can help to realize a high-quality power combination of the full polarization radiation field. Furthermore, the DNZ photonic crystal (PC) is designed and applied to approach full polarization power combination with multiple sources arranged in a complex pattern. In addition, the radiation field patterns of full polarization power combination could be easily controlled by changing the shape or boundary conditions of the PC.

Plasmonic tweezers have become an important tool for the capture, manipulation, and characterization of nanoparticles (NPs), biomolecules, and viruses. However, the physical environment in the microscale strongly affects the trapping performance of plasmonic nanostructures. We demonstrated the trapping of gamma-aminobutyric acid (GABA) functionalized gold NPs at different solution temperatures and viscosities. Experimental results show that the trapping stiffness decreases from 0.3 to 0.1 fN/nm as the temperature increases from 25°C to 37°C. For solutions with higher viscosity, the trapping stiffness increases but the trapping efficiency would be reduced due to hindered movement of particles.

In wireless communication, two pertinent performance metrics of data rate and bandwidth (BW) play a vital role. Wireless technology must be tuned to reach the most prevalent possible data rate. The usage of terahertz (THz) frequency has recently increased in various applications due to its non-ionizing characteristics. It is possible to attain a high data rate even in the terabits per second range using THz technology. The proposed antenna incorporates a photonic crystal (PhC) structure in addition to the THz technology to improve its performance. We propose a unique pie slotted patch (PSP) antenna using the simulation tool and explore the antenna attributes. We optimize the proposed PSP antenna in three cases by optimizing the PhC air hole shapes, lattice value, and dimensions. The triangular air hole PhC model shows that the best PSP antenna has a −71.35-dB return loss, a 1.0095 voltage standing wave ratio (VSWR), and a 9.87-dBi gain at a frequency of 2.04 THz. The proposed PSP antenna helps to deliver effective data rates in wireless communications and other various streams.

Symmetry-protected bound states in the continuum (BIC) can be transformed into quasi-BIC (QBIC) with an ultra-high quality factor so that the external excitation can couple with them. Typically, notches are commonly induced by introducing in-plane broken symmetry. We introduce a metasurface composed of dimer nanobars with out-of-plane broken symmetry. It is demonstrated that band-folding QBICs can be realized by introducing notches along z-direction. The effect of polarization on coupling between the QBIC mode and incident light is also studied. The polarization response of QBIC indicates that the linewidth of the resonance peak rather than the resonance intensity is regulated by the azimuth angle and shows an inverse square relationship, which is not mentioned in previous studies. Analysis of far-field contributions from multipole decomposition and electromagnetic field distribution reveal that the dominant contributors to the QBIC are the magnetic dipole moment and electric quadrupole. Our results may provide a route for enhancing light-matter interaction.