ACS Photonics最新文献

Vectorial Doppler metrology exploits spatially varying polarization structures to enable direction-sensitive angular velocimetry, offering capabilities beyond those of scalar Doppler schemes. However, applying such vectorial strategies within nonlinear detection frameworks remains challenging, as conventional frequency-conversion processes are inherently polarization-dependent and tend to distort the vectorial topology that encodes directional Doppler information. In this work, we overcome this fundamental limitation by introducing a spatial-polarization-independent upconversion scheme that preserves the full vectorial structure of rotational Doppler signals. This allows for infrared Doppler polarization signals to be conformally translated into the visible domain while retaining their directional sensitivity. Within this preserved vectorial framework, we realize direction-resolved rotational velocimetry through two complementary detection approaches: a commonly employed polarization differential detection method and a newly proposed polarization heterodyne detection scheme that provides a compact and robust time–frequency route to retrieving the rotation direction. These results establish a practical pathway for vectorial Doppler sensing under nonlinear frequency conversion and highlight the broader utility of multidimensional optical degrees of freedom for robust, high-fidelity multiparameter measurement.

Second-order nonlinear optical materials enable frequency doubling of light (second-harmonic generation, SHG), which is essential for optoelectronic applications ranging from materials characterization to quantum technologies. However, comparing SHG performance across materials remains challenging as the second-order nonlinear susceptibility, χ⁽²⁾, spans several orders of magnitude and strongly depends on the band gap, E_g. To address this, we empirically validate a theoretical upper bound on χ⁽²⁾ using new databases of ab initio-computed nonlinear optical (NLO) properties. We then formulate a normalized descriptor, d̂, which expresses the NLO response of a material relative to the band gap-dependent physical limit. We show that d̂ exhibits a similar distribution across a wide range of band gap energies. We also demonstrate that the formalism used to compute χ⁽²⁾ leads to a competition with methodological uncertainty driven by band gap predictions to systematically alter the prediction of the second-order nonlinear response. The universality of d̂ supports its use as a robust, generalizable metric for chemistry-informed machine-learning models and quantification of NLO performance, enabling accelerated materials discovery and optimization across broad application frequencies.

Nondiffracting optical beams are essential tools in photonics, offering robust light transport, super-resolution imaging, and spatiotemporal control. While nonlocal metasurfaces have been proposed for structured-light generation due to their broad angular spectral dispersion and topological characteristics, experimental generation of nondiffracting beam with nonlocal metasurfaces have not been previously demonstrated. Here, we experimentally realize vortex Bessel beams using a nonlocal metasurface and uncover a link between nondiffracting beam generation and the curvature of the photonic bands. Depending on the sign of band curvature, the beams exhibit spatial asymmetry in nondiffraction, emerging either in front of or behind the metasurface. This asymmetry arises from a radial-phase gradient in momentum space, which induces an effective space compression or expansion. Furthermore, we demonstrate wavelength-dependent tunability of the beam diameter and propagation distance and show an order-of-magnitude enhancement in propagation distance compared to conventional Laguerre–Gaussian modes. These results establish nonlocal metasurfaces as a powerful platform for compact, tunable, and spatiotemporally controlled nondiffracting light.

High-speed, compact photodetectors are essential for silicon photonics. Germanium and III–V materials are well-established for integrated photodetection. However, the heterogeneous integration with silicon waveguides generally increases cost and fabrication complexity. All-silicon photodetectors offer a monolithic alternative, but their performance is fundamentally constrained by the transparency of silicon at telecom wavelengths and the intrinsic trade-off between responsivity and bandwidth. Here, we propose and experimentally demonstrate a response-engineered tandem microring photodetector that overcomes this limitation. By detuning resonances to form a partially overlapped dual-peak response, the device can support strong optical field enhancement and large optoelectronic bandwidth. The foundry-fabricated photodetector exhibits a 3 dB bandwidth of 40 GHz, a responsivity of 0.32 A/W, and a dark current of 300 nA at −8.4 V bias. Record-high data reception rates of 128 Gb/s NRZ and 200 Gb/s PAM-4 are experimentally demonstrated, showing the potential of this approach for high-speed optical interconnects.

The size-dependent lasing behavior and carrier dynamics of CsPbBr₃ perovskite micro/nanostructures remain inadequately explored, particularly across the critical subwavelength to micrometer scale range. Herein, we systematically investigate the lasing performance and recombination pathways of CsPbBr₃ nanowires/microwires (NWs/MWs) and nanoplatelets/microplates (NPs/MPs) with sizes spanning 0.25–12.7 μm. As the crystal size increases, the lasing emission wavelength exhibits a significant red shift, governed primarily by cavity-mode resonance rather than quantum confinement. A unified quantitative model is developed to correlate the lasing wavelength with crystal size, incorporating effective refractive index variations and mode competition effects. The recombination mechanism converts from trap-assisted recombination to bimolecular and Auger recombination with an increase in pump fluence. The competitive recombination pathways of excitons and free charge carriers evolve dynamically with size. Experimental and computational results reveal that variations in trap state density, carrier diffusion length, and exciton concentration modulate the size-dependent recombination coefficients k₁, B, and C. Furthermore, the size-dependent carrier lifetime, trap state density, carrier density, carrier diffusion length, absolute PLQY, and cutoff wavelength are evaluated. Subwavelength-scale CsPbBr₃ achieves lasing emission through synergistic mechanisms of carrier localization, low scattering loss, low defect state density, and high optical gain. This work establishes a foundational framework for designing size-tunable perovskite lasers and advances the understanding of scale-dependent photophysics in semiconductor gain media.