arXiv subjects

Junjia Wang

Publications and source records attributed to Junjia Wang.

6 recordsLinked to original sources

arXiv2026

Tailoring Quasi-Bound States in the Continuum for Infrared Photodetection in Black Phosphorus

High-performance infrared photodetection underpins various applications spanning surveillance, environmental monitoring, optical communications and biomedical imaging. However, conventional bulk detectors remain limited by poor spectral tunability, mechanical rigidity, and high dark currents, motivating the pursuit of low-dimensional material platforms such as graphene and transition metal dichalgenides. Black phosphorus (BP) is particularly compelling in this context, owing to its thickness-tunable direct bandgap, high carrier mobility, and pronounced in-plane anisotropy. Nevertheless, its atomically thin nature inherently restricts light absorption, posing a fundamental bottleneck for device performance. Here, we demonstrate quasi-bound states in the continuum (quasi-BICs) within a dielectric metasurface integrated with BP, enabling strongly enhanced and spectrally selective light-matter interactions. By introducing controlled symmetry breaking at the unit-cell level, high-quality-factor resonances are realized, resulting in pronounced electromagnetic field confinement within the BP layer. This resonant enhancement substantially increases photocarrier generation while preserving the intrinsic polarization anisotropy of BP, which elucidates a robust pathway for overcoming the optical absorption bottleneck in anisotropic 2D optoelectronics via quasi-BIC platforms.

physics.optics↗

arXiv2025

A Value Mapping Virtual Staining Framework for Large-scale Histological Imaging

The emergence of virtual staining technology provides a rapid and efficient alternative for researchers in tissue pathology. It enables the utilization of unlabeled microscopic samples to generate virtual replicas of chemically stained histological slices, or facilitate the transformation of one staining type into another. The remarkable performance of generative networks, such as CycleGAN, offers an unsupervised learning approach for virtual coloring, overcoming the limitations of high-quality paired data required in supervised learning. Nevertheless, large-scale color transformation necessitates processing large field-of-view images in patches, often resulting in significant boundary inconsistency and artifacts. Additionally, the transformation between different colorized modalities typically needs further efforts to modify loss functions and tune hyperparameters for independent training of networks. In this study, we introduce a general virtual staining framework that is adaptable to various conditions. We propose a loss function based on the value mapping constraint to ensure the accuracy of virtual coloring between different pathological modalities, termed the Value Mapping Generative Adversarial Network (VM-GAN). Meanwhile, we present a confidence-based tiling method to address the challenge of boundary inconsistency arising from patch-wise processing. Experimental results on diverse data with varying staining protocols demonstrate that our method achieves superior quantitative indicators and improved visual perception.

eess.IV↗

arXiv2024

High Performance Graphene Integrated Photonics Platform Enabled by Gold-assisted Transfer

Graphene is promising for nanoscale, efficient, ultra-fast photo- and opto-electronic devices because of its remarkable electrical and optical properties, such as fast electron relaxation and heat dissipation. Here, we realize high-performance graphene integrated photonics platform enabled by gold-assisted transfer. Thanks to our optimized transfer technique, we fabricate and demonstrate (1) a microscale thermo-optic modulator with a tuning efficiency of 0.037 nm/mW and high heating performance of 67.4 K$μm^{3}mW^{-1}$ on a small active area of 7.54 $μm^{2}$ and (2) a graphene electro-absorption modulator featuring an high modulation bandwidth up to 26.8 GHz and a high-speed data rate reaching 48 Gb/s, and (3) a graphene Mach-Zehnder interferometer modulator with a high normalized modulation efficiency of 0.027 dBV$^{-1}μm^{-1}$. Our graphene integrated photonics platform has far superior performances compared to state of the art in terms of efficiency, low process complexity, and compact device footage. Thus, our approach and results provide the background for the realization of high-performance integrated photonic circuits with CMOS compatibility.

physics.optics↗

arXiv2024

High sensitivity and large scanning range optical antennas enabled by multi-casting ridge-waveguide subwavelength structure arrays

With the rapid development of large-scale integrated photonics, optical phased array (OPA) is an effective way to realize highly integrated, stable and low-cost beam control system. Achieving a large field of view (FOV) in the longitudinal direction without increasing fabrication cost and system complexity is still a significant challenge in OPA antennas. Here, a high sensitivity and large scanning range antenna based on subwavelength structure array is proposed to enhance the longitudinal scanning and free-space radiating efficiency by using the ridge-waveguide structure and backward-emitting. A millimeter-long grating antenna with a far-field beam divergence of 0.13° and a wavelength sensitivity of 0.237°/nm is experimentally demonstrated. Furthermore, by using different sideband periods, we introduce a multi-casting grating antenna with a large scanning range up to 42.6°. The proposed devices show significant improvement in longitudinal wavelength sensitivity compared with the typical waveguide grating antennas.

physics.optics↗

arXiv2019

Mid-infrared polarized emission from black phosphorus light-emitting diodes

The mid-infrared (MIR) spectral range is of immense use for civilian and military applications. The large number of vibrational absorption bands in this range can be used for gas sensing, process control and spectroscopy. In addition, there exists transparency windows in the atmosphere such as that between 3.6-3.8 $μ$m, which are ideal for free-space optical communication, range finding and thermal imaging. A number of different semiconductor platforms have been used for MIR light-emission. This includes InAsSb/InAs quantum wells, InSb/AlInSb, GaInAsSbP pentanary alloys, and intersubband transitions in group III-V compounds. These approaches, however, are costly and lack the potential for integration on silicon and silicon-on-insulator platforms. In this respect, two-dimensional (2D) materials are particularly attractive due to the ease with which they can be heterointegrated. Weak interactions between neighbouring atomic layers in these materials allows for deposition on arbitrary substrates and van der Waals heterostructures enable the design of devices with targeted optoelectronic properties. In this Letter, we demonstrate a light-emitting diode (LED) based on the 2D semiconductor black phosphorus (BP). The device, which is composed of a BP/molybdenum disulfide (MoS$_2$) heterojunction emits polarized light at $λ$ = 3.68 $μ$m with room-temperature internal and external quantum efficiencies (IQE and EQE) of ~1$\%$ and $\sim3\times10^{-2}\%$, respectively. The ability to tune the bandgap, and consequently emission wavelength of BP, with layer number, strain and electric field make it a particularly attractive platform for MIR emission.

physics.app-ph↗

arXiv2019

Spectral responsivity and photoconductive gain in thin film black phosphorus photodetectors

We have fabricated black phosphorus photodetectors and characterized their full spectral responsivity. These devices, which are effectively in the bulk thin film limit, show broadband responsivity ranging from <400 nm to the ~3.8 $μ$m bandgap. In the visible, an intrinsic responsivity >7 A/W can be obtained due to internal gain mechanisms. By examining the full spectral response, we identify a sharp contrast between the visible and infrared behavior. In particular, the visible responsivity shows a large photoconductive gain and gate-voltge dependence, while the infrared responsivity is nearly independent of gate voltage and incident light intensity under most conditions. This is attributed to a contribution from the surface oxide. In addition, we find that the polarization anisotropy in responsivity along armchair and zigzag directions can be as large as 103 and extends from the band edge to 500 nm. The devices were fabricated in an inert atmosphere and encapsulated by Al$_2$O$_3$ providing stable operation for more than 6 months.

physics.app-ph↗