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Nonlinear optics has generated a wide range of applications in the fields of optical communications, biomedicine, and materials science, with nonlinear conversion efficiency serving as a vital metric for its progress. However, the weak nonlinear response of materials, high optical loss, and inhomogeneous distribution of the light field hamper the improvement of the conversion efficiency. We present a composite grating waveguide structure integrated into a Bragg reflector platform. This design achieves high Q in the spectral range by exploiting the unique properties exhibited by the bound states in the Bloch surface wave-enhanced continuum, and efficient second-harmonic generation by close-field amplification with the optical field tightly localized in a nonlinear material. By manipulating the symmetry of the grating, a precise tune over the near field within a designated wavelength range can be achieved. Specifically, we select a photonic crystal configuration supporting surface waves, employing TE polarization conditions and an asymmetry factor of −0.1 between the composite gratings. This configuration resonates at a fundamental wavelength of 783.5 nm, exhibiting an impressive Q-factor of 106. Notably, at an incident light intensity of 1.33 GW/cm2, we achieve a normalized electric field strength of up to 940 at the fundamental frequency and a second-harmonic conversion efficiency of up to 6 × 10−3, significantly amplifying the second-harmonic response. The proposed configuration in this investigation has the potential to be integrated into the field of nonlinear optics for sensing frequency conversion applications.

Conventional photodetectors overly pursue high light‐to‐electric conversion efficiency under weak light stimulation, while disregarding the saturated absorption‐induced blinding effect upon strong light, and achieving efficient photodetection covering a large power range remains a great challenge. In this work, MoS2/BaTiO3 heterostructures are constructed through a low‐cost exfoliation and transfer method combined with spin‐coating. The photoresponse behaviors before and after assembling the BaTiO3 nanoparticles onto the MoS2 nanoflake are investigated, indicating that the high conductivity of MoS2 and ferroelectricity of BaTiO3 can complement each other to improve the photoresponse of the hetero‐integrated device, acquiring a high photoresponsivity of 17402 A W−1 under 0.2 nW irradiation, and a significant 570 µA photocurrent under 8 mW irradiation, realizing a large linear dynamic range index of 152 dB, which is at the top level among layered semiconductor‐based detectors. Moreover, strong power near‐infrared light can be up‐converted to the visible band through the nonlinear effect of BaTiO3, subsequently absorbed by the MoS2 and contributing to the photocurrent, providing a solution to combat and alleviate the saturated absorption issue in photodetection. This work marks a significant advancement in achieving robust high‐performance photodetection by hetero‐integrating 2D materials with ferroelectrics. [ABSTRACT FROM AUTHOR]

In this study, a detector is developed using deuterated L‐alanine doped triglycine sulfate (DLATGS) crystals capable of detecting circularly polarized light (CPL) and various polarization states. As a primary pyroelectric detection crystal, DLATGS has exhibited notable optical responses to both linearly and circularly polarized light during the tests, demonstrating a favorable polarization ratio of 3.86 and an anisotropic factor glph${g}_{lph}$ of 0.529. The research discovers the broad‐spectrum bulk photovoltaic (BPVE) characteristics in DLATGS, highlighting its potential for CPL detection. By integrating linear and circular bulk photovoltaic effect theories (LBPV and CBPV), the crystal's ability to differentiate between various polarization modes, including left‐/right‐handed polarized light, is confirmed. The BPVE and pyro‐phototronic coupling responses is characterized, laying a theoretical foundation for a rare pyroelectric effect‐based multifunctional polarization detector. The overall consistency of phenomena and theoretical framework bridges the gap between theoretical predictions and experimental validation. This work not only advances the understanding of DLATGS crystals but also sets the stage for further exploration into chiral materials and the development of TGS‐type crystals in future photoelectronic detectors. [ABSTRACT FROM AUTHOR]

High responsivity ultraviolet (UV) photodetectors (PDs) are essential for abundant civilian and military applications. Gallium nitride (GaN) has emerged as an ideal material for UV PD fabrication due to its favorable properties. However, the quality of GaN epitaxial layers significantly impacts device performance and reliability. Sapphire-based GaN epitaxial growth technology enables the realization of high-quality GaN epitaxial layers, making it the preferred choice for GaN substrates. Nonetheless, the thermal expansion coefficient mismatch between sapphire and GaN can lead to crystal mismatch and stress accumulation at high temperatures, affecting device performance and reliability. In contrast, lithium niobate (LiNbO3) exhibits similar coefficients of thermal expansion to GaN, mitigating crystal mismatch and stress accumulation issues. Here, we report the realization of a GaN UV PD by laminating GaN membrane onto ferroelectric LiNbO3 through selective electrochemical etching of the sapphire-based GaN epitaxial film. The LiNbO3-based GaN PD achieves a specific high on/off ratio of 107. At a 5 V bias voltage, the device exhibits a high peak responsivity of 1.712 × 103 A/W under 325 nm laser illumination. Furthermore, the device demonstrates excellent performance for polarization light detection, with a polarization ratio of approximately 54.95. Exploiting the local ferroelectric polarization of x-cut LiNbO3, the photogenerated electron–hole pairs in GaN are efficiently separated by the electrostatic field from the polarization of ferroelectric LiNbO3, resulting in enhanced light-to-electric conversion efficiency. Our work presents a method for fabricating high responsivity GaN-based UV PD, showcasing the potential of integrating ferroelectric LiNbO3 to enhance device performance. [ABSTRACT FROM AUTHOR]

Second harmonic generation (SHG) with a material of large transparency is an attractive way of generating coherent light sources at exotic wavelength range such as VUV, UV and visible light. It is of critical importance to improve nonlinear conversion efficiency in order to find practical applications in quantum light source and high resolution nonlinear microscopy, etc. Here an enhanced SHG with conversion efficiency up to 10−2% at SH wavelength of 282.7 nm under 11 GW/cm2 pump intensity via the excitation of anapole in lithium niobite (LiNbO3, or LN) nanodisk through the dominating d33 nonlinear coefficient is investigated. The anapole has advantages of strongly suppressing far-field scattering and well-confined internal field which helps to boost the nonlinear conversion. Anapoles in LN nanodisk is facilitated by high index contrast between LN and substrate with properties of near-zero-index via hyperbolic metamaterial structure design. By tailoring the multi-layers structure of hyperbolic metamaterials, the anapole excitation wavelength can be tuned at different wavelengths. It indicates that an enhanced SHG can be achieved at a wide range of pump light wavelengths via different design of the epsilon-near-zero (ENZ) hyperbolic metamaterials substrates. The proposed nanostructure in this work might hold significances for the enhanced light–matter interactions at the nanoscale such as integrated optics.

Two-dimensional material tungsten diselenide (WSe2) nanosheets are coated on a microfibre knot resonator (MKR) to achieve an all-optical power modulation functionality. On account of the strong absorption property of WSe2 and the resonance enhancement properties of MKR, the transmitted optical power of signal light within the WSe2-based MKR can be effectively modulated. The sensitivities of light–control–light experiments with 405- and 660-nm lasers are as high as 0.32 and 0.12 dB/mW, respectively. The sensitivities and power tuning can be enhanced by a higher resonance Q and a larger extinction ratio of MKR. In terms of the response time, the average rise and fall times are 3.5/3.7 and 3.5/4 ms with 405- and 660-nm lasers, respectively. This proposed structure is expected to achieve potential applications in all-fibre-optic–based tunable device such as optical modulator, detector, and so on.

Two‐dimensional (2D) materials are widely used in numerous optoelectronic devices due to their ultra‐thin dimensions and versatile surfaces. However, less attention is paid to distinguishing the light‐matter interactions along the vertical and horizontal paths within the same 2D lattice, as well as comparatively investigating the optoelectronic behaviors between the sensitive top and bottom surfaces. Here, a dual‐crossbar configured architecture is designed and constructed based on Bi2O2Se semiconductor, featuring highly compact three‐in‐one assembly, namely bottom surface horizontal (BSH), middle sandwich vertical (MSV) and top surface horizontal (TSH) devices. The MSV with nanoscale channel possesses efficient separation and transportation of the photogenerated electrons and holes, responding faster to the light stimulation and compared favorably to the BSH and TSH devices. The optoelectric behaviors of the BSH device can be regulated by the characteristics of the substrate due to closer contact. Nevertheless, the performance of the TSH device is more sensitive to the environment, such as dopant absorption and heat dispersion, thus enabling the non‐volatile photoresponse and can be employed as an artificial optoelectronic synapse. This work highlights the importance of designing the device architecture based on the intrinsic structural advantages of 2D materials, paving the way toward integrated optoelectronics. [ABSTRACT FROM AUTHOR]

In this work, a doubly resonant photonic crystal (PhC) cavity is proposed to enhance second harmonic generation (SHG) efficiency and photon pair generation rate (PGR). Through the exploration of geometry parameters, a band-edge mode within the light cone is identified as the first harmonic (FH) mode, and a band-edge mode outside the light cone is designated as the second harmonic (SH). Subsequently, by increasing the layers of the core region, a heterostructure PhC cavity is designed. The results showcase a doubly resonant PhC cavity achieving a 133/W SHG efficiency and a photon pair generation rate of 3.7 × 108/s. The exceptional conversion efficiency is attributed to the high quality factors Q observed in the FH and SH modes with values of approximately 280,000 and 2100, respectively. The remarkably high Q factors compensate for nonlinear efficiency degradation caused by detuning, simultaneously making the manufacturing process easier and more feasible. This work is anticipated to provide valuable insights into efficient nonlinear conversion and photon pair generation rates. [ABSTRACT FROM AUTHOR]

As a two-dimensional (2D) material, black phosphorus (BP) has attracted significant attention owing to exotic physical properties such as low-energy band gap, high carrier mobility, and strong in-plane anisotropy. The striking in-plane anisotropy is a promising candidate for novel light-matter interaction. Here, we investigate the photonic spin Hall effect (PSHE) on a monolayer of BP. Due to the in-plane anisotropic property of BP, the PSHE is accompanied with Goos-Hänchen and Imbert-Fedorov effects, resulting in an asymmetric spin splitting. The asymmetric spin splitting can be flexibly tuned by the angle between the incident plane and the armchair crystalline direction of BP and by the carrier density via a bias voltage. The centroid displacements of two opposite spin components of the reflected beam along directions parallel and perpendicular to the incident plane can be considered as four independent channels for information processing. The potential application in barcode-encryption is proposed and discussed. These findings provide a deeper insight into the spin-orbit interaction in 2D material and thereby facilitate the development of optoelectronic devices in the Terahertz region.

Lithium niobate (LN) is widely used in various optoelectronic systems due to its structural anisotropy and ferroelectric feature, which is one of the most essential platforms for next‐generation integrated optoelectronics. However, the insulating and optically transparent characteristics of LN have greatly limited the application in photodetection. Here, a high‐performance LN/WS2 based photodetector is achieved through a van der Waals integration strategy in which the pyroelectric property of LN and the moderate bandgap of WS2 are well combined. Upon light illumination, the light induced carriers in WS2 would increase and the pyroelectric charges of LN will cross the interfacial gap and asymmetrically inject into the WS2, creating an n−/n+ homojunction, thus improving the on‐state current. Under dark conditions, the sudden removal of the laser would introduce an instantaneous enhancement of polarization in the LN lattice, leading to an improved confinement on the remaining carriers in WS2, achieving a lower dark current. In this regard, the configurated device acquires a high on/off ratio more than 104 under zero bias, which represents the best among all the reported LN‐based photodetectors. This work realizes the complementary integration of 2D materials and ferroelectric LN and provides a feasible way for high‐performance photodetectors based on the LN platform. [ABSTRACT FROM AUTHOR]