JNP thanks the reviewers who served the journal in 2023.

Photonic integrated circuits (PICs) have attracted great attention as promising platforms for high-data-rate communications and high-performance computing. For the PICs, photonic devices with compatible materials, compact footprint, high-performance, and sophisticated functionalities are necessary building blocks. Design optimization to implement such devices for target applications and requirements are of critical importance. In this respect, inverse design methods, including iterative optimizations and deep neural networks, have demonstrated significant advantages over the traditional simulation-based trial-and-error optimization approach. We provide an overview of the recent progress on the inverse designs for the integrated photonic devices. The principles and procedure of the inverse design methods are presented and discussed, followed by a summary of the methods employed for specific integrated photonic devices in different integrated photonics material platforms. Finally, topics of future applications and fabrication constraints for the inverse design methods are discussed.

This work presents a refractive index sensor based on Bloch surface waves (BSW) with high sensitivity and quality factor (Q). The sensor utilizes a one-dimensional photonic crystal TiO2/MgF2 as a distributed Bragg reflector and employs a LiNbO3 thin film as the top defect layer to excite BSW through a Kretschmann prism. Numerical simulations using the rigorous coupled wave analysis method are conducted to explore various prism configurations, revealing that low refractive index prisms yield superior performance for BSW sensors. The designed sensor achieves a sensitivity of 1600 nm/RIU (or 938 °/RIU) and is analyzed for its full-width at half-maximum and quality factor (Q), with the sensor’s Q value reaching 8000 /RIU (or 13595 /RIU). Through manufacturing error analysis, it was found that the designed sensor has good mechanical robustness, is easy to manufacture, and is also easy to integrate. The results show that the LiNbO3 nonlinear tunable material has great application prospects in the field of refractive index sensors.

The escalating demand for cost-effective, flexible, and solution-processed materials in infrared (IR) photodetection presents a compelling alternative to current epitaxially grown optoelectronic technology. Colloidal quantum dots (CQDs) have emerged as a versatile platform for optoelectronic device fabrication, offering affordability, low-temperature synthesis, and scalability. Specifically, mercury chalcogenide CQDs exhibit notable intraband absorption in the mid-IR region. In this study, we explore an intraband HgSe-HgTe CQD photodetector structure tailored for mid-IR light detection. Through numerical optimization, we engineer detectivity by varying key design parameters—the film doping density, CQD diameter, and number of periods in the active layer—under different temperatures and biases. Results indicate that, at 60 K and 1 V bias, our optimally designed HgSe-HgTe CQD IR photodetector attains a peak detectivity of 8.14×1010 Jones for a film doping density of 1019 cm−3 of HgSe CQDs, 9.34×1010 Jones for HgSe CQDs with a 4.8 nm diameter, and 8.72×1010 Jones for 9 periods of HgSe-HgTe CQDs.

The interaction between the chiral light and matter is vital to construct on-chip multi-functional photonic circuits. The well-known spin-orbit interaction has obtained significant attention in manipulation of light with different circular polarization states. We propose a robust Y-type surface plasmon nano-waveguide structure to effectively sort spin-dependent photons. The optimized simulation results demonstrated that the waveguide modes excited by circularly polarized light with different spin states can be selectively coupled to one of two branching waveguides, with a unidirectionality efficiency up to 0.95. This research may open up new ways for the on-chip implementation of complex photonic functions, nano-photonic circuits, and nano-optical manipulation.

Since the emergence of perovskite as an exceptional light absorbing material, it has made significant advancements in enhancing the efficiency of solar cells. Building upon this foundation, the reconfiguration of internal optical properties within perovskite holds the promise of further improving efficiency. We investigated the influence of metallic aluminum triangular nanostructures on absorption rates. Our findings indicate that the incorporation of stacked aluminum triangular nanostructures into perovskite thin films, along with controlled adjustments in the side length, can significantly enhance absorption rates. In conclusion, comparative tests revealed a remarkable 51% increase in the solar spectrum absorption rate for single layer perovskite thin film photovoltaic cells with a thickness of 200 nm.

An increasing amount of attention is being paid to guided-mode resonance (GMR) sensors since they can effectively detect small refractive indices (RIs) changes due to their narrow spectral linewidth and high efficiency. In this work, a binary, all-dielectric, asymmetric GMR (A-GMR) sensor structure with enhanced sensitivity and narrowed resonant linewidth is proposed to substantially improve the figure of merit (FOM) with respect to symmetric counterparts. To achieve the best performance, particle swarm optimization is employed to optimize the structural parameters. Furthermore, the proposed GMR sensor is compared with dielectric symmetric GMR sensors. High bulk sensitivity of 3157.6 nm/RIU, full width at half maximum down to 0.076 nm, and FOM of 41547.368 (RIU)−1 have been achieved for the A-GMR sensor, showing high-performance RI sensing.

Light propagation and acoustic vibrations can be controlled by designing the bandgap of phoxonic crystals, which support photonic and phononic bandgaps simultaneously. In this study, we numerically investigated the optical and mechanical properties of a clover-shaped 6H-SIC crystal microcavity. The results indicate that the frequency range of the phononic bandgap can be manipulated by adjusting the geometry of the structure, resulting in a wide phononic bandgap over 12 GHz centered at 30.8 GHz. The structure also supports strong localized optical modes for visible light with a Q-factor over 143. Within the photonic and phononic bandgaps of the phoxonic crystal, the structure can reduce mechanical vibrations and support a confined optical mode that can be used for trapping nanoparticles.

High-performance sensors can be efficiently realized with an all-dielectric metasurface using high-Q-factor Fano resonance. In this study, a numerical analysis of an all-dielectric metasurface with two square holes and one rectangular hole was conducted. Multiple Fano resonances with a high Q-factor and modulation depth were excited by a toroidal dipole, an electric quadrupole, and a magnetic dipole by breaking the symmetry of the structure. According to the computed results, the modulation depth approached 100%, and the maximum Q-factor reached 90,048. The sensing performance of the structure is also discussed. The structure had a maximum sensitivity and figure of merit of 275 nm/RIU and 1833 RIU−1, respectively. Owing to the unique structure, multiple Fano resonances can be achieved, with applications in multiwavelength communication, multichannel nanosensors, and optical modulators. These resonances have high Q-factors, high modulation depths, and small linewidths.

A Ge2Sb2Te5 (GST)-based microring resonator is designed and analyzed for optical switching-based applications. First, the optical properties of GST material having thicknesses of 130 to 230 nm on two commonly used substrates, i.e., silicon (Si) and silicon dioxide (SiO2), are investigated in detail. The phase-change property of GST plays an important role in tuning the resonant wavelength, absorption, and transmission loss in the ring resonator as its crystalline state has a higher refractive index (RI) compared with the amorphous state. Due to the phase-change property of the GST material, the effective RI of the waveguide core changes. A patch of GST is embedded on a ring resonator to optimize the response of light coupled in the ring and straight waveguide, that is tunable between its amorphous phase (a-GST) and crystalline (c-GST) phase. The difference in refractive indices between the two states of a phase-change material (PCM) renders it an optimal choice for the optical active devices used in light modulation and switching applications. The GST is employed as an active material in the proposed structure as it is significantly stable and results in reduced insertion loss (IL) compared with other PCMs. In the proposed design of the ring resonator, the finite-difference time-domain simulation demonstrates high extinction ratios of 16.05 and 20.50 dB at the THROUGH and DROP ports, respectively. Moreover, the low insertion losses (IL) of 0.33 dB at the THROUGH port in crystalline phase and 0.8 dB at the DROP port in amorphous phase, have been observed. The Q-factor of the ring resonator without a GST patch is 5.18×105, whereas with a GST patch, it is 5.13×105 and 1.28×105 in the amorphous and crystalline phases, respectively.

In this work, HNbxTa1-xWO6 (x=0, 0.3, 0.5, 1) nanosheets were successfully synthesized by an in-suit doping strategy at the molecular level and an exfoliation-restacking process. The crystal phase structures, surface morphologies, and chemical components of the obtained HNbxTa1-xWO6 nanosheets were systematically characterized by X-ray diffraction patterns, laser Raman spectroscopy, scanning electron microscopy, ultraviolet–visible diffuse reflectance spectroscopy and N2 adsorption-desorption measurements. The adsorption and photocatalytic degradation of RhB aqueous solution under dark and simulated sunlight irradiation were investigated, respectively. The adsorption results demonstrated that the large total pore volume and strong acidity are favorable for the adsorption of RhB, and the photocatalytic results showed that the introduction of Ta element greatly improved the photocatalytic activities of the as-prepared HNbxTa1-xWO6 nanosheets. Among the HNbxTa1-xWO6 nanosheets, HTaWO6 nanosheet has the highest photocatalytic activity for RhB degradation with a rate constant of 1.62×10−2 min−1. According to the photocatalytic result, it can be concluded that the use of in-suit doping to control the energy band structure is an effective method for designing efficient photocatalysts.

Silicon micro-ring resonator-based generation of all-optical (2×2) Walsh–Hadamard code is proposed. The energy-efficient, ultra-high-speed, and compact nature of micro-ring resonator-based devices is essential for optical computing. Both MATLAB and the Ansys Lumerical finite difference time domain (FDTD) approach are used to implement the generation of all-optical (2×2) Walsh–Hadamard code. The proposed design is simulated at about 260 Gbps. In the recommended circuit, the needed pump power for switching is merely 0.84 mW, which is extremely little in contrast. The “figure of merits” of the proposed design is evaluated through numerical simulation. The obtained contrast ratio and extinction ratio are considerably greater at 25.24 and 14.63 dB, respectively. On the other hand, the achieved amplitude modulation of 0.13 dB is extremely low. The on-off ratio for a single micro-ring resonator is 36.9 dB.

Nitrogen and sulfur co-doped green fluorescent carbon dots (G-CDs) with quantum yield (QY) of 28.26% were synthesized by hydrothermal method with p-phenylenediamine and thiosemicarbazone as precursors. The synthesized G-CDs exhibit good sensitivity and anti-interference ability for detecting copper ion (Cu2+) by fluorescence quenching (λex=390 nm, λem=535 nm) with a linear range of 20 to 200 μM and the limit of detection of 4.8 μM. This analytical method has been applied to detect Cu2+ of the local lake with good accuracy and recovery.

With the continuous improvement of detection technology, higher requirements are put forward for infrared camouflage. Conventional low-emissivity materials have serious thermal instability, which increases the risk of detection. There is an urgent need to investigate more efficient infrared stealth materials. We design a metamaterial selective broadband emitter that utilizes multi-resonance coupling of metal patterns for infrared stealth. The proposed design exhibits low emissivity in the infrared atmosphere windows (3 to 5 μm and 8 to 14 μm) for infrared suppression and high emissivity in the non-infrared atmosphere window (5 to 8 μm) for radiative cooling. We introduce a supplementary design for high-temperature environments to meet a broader application need. Moreover, the low angle-dependence of the metamaterial emitter enables it to maintain broadband absorption characteristics even under large-angle incidence. This proposed approach serves as an effective supplement to the design of metamaterial broadband emitters and holds great potential for applications in infrared stealth, radiative cooling, thermal detection, sensors, thermophotovoltaics, and various other fields.