Superconducting quantum capacitance detectors (QCDs) have emerged as among the most sensitive terahertz (THz) photon detectors, positioning them as promising detector components for next-generation cryogenic telescopes. However, their limited dynamic range (DR, ∼32 dB) and low saturation power (∼0.1 fW) have hindered their broader applications, such as in THz astronomy, high-resolution spectroscopy, and microscopic imaging. Here, we propose a mechanism that enables controllable adjustment of the sensitivity and DR of THz QCDs, supported by both theoretical modeling and experimental validation. We developed a QCD design that features a fork-shaped gate capacitor and a high-efficiency grid absorber. The resulting devices exhibit a noise equivalent power of 5.0 × 10−20 W/Hz1/2 and a DR of 40 dB, providing a favorable balance between sensitivity and DR and advancing the practical application of QCDs in future THz applications.
Multimode vertical-cavity surface-emitting lasers (VCSELs) often display broad spectra, increased beam divergence, and limited control over the spatial profile of the emitted light. To address this, we introduce VCSELs with lithographically defined ring-shaped tunnel-junction apertures, which spatially tailor gain and optical confinement. Spectrally resolved measurements and simulations show that the ring geometry fundamentally reshapes the supported modal set. This reduces spectral width and far-field divergence compared to conventional circular apertures. At the same time, Gaussian-like far-field intensity profiles are achieved even in nominally multimode devices. Comparable output power is obtained from ring and circular apertures with identical external diameters, despite the significantly reduced active area of the ring geometry. This confirms enhanced mode–carrier overlap and improved thermal behavior. Beyond reshaping multimode emission, the same ring-aperture platform is combined with engineered surface-relief losses and gain design to favor selected transverse modes. Through the interplay of spatially selective gain injection and tailored modal loss, we demonstrate stable single-mode emission with output powers exceeding 8 mW. Rather than relying only on suppression of unwanted higher-order modes, this approach enables transverse modes to be reshaped, stabilized, and selectively exploited. These results establish VCSELs with ring lithographic apertures as a scalable route toward high-power beam shaping and structured-light generation in semiconductor cavities.
Three-dimensional topological light fields extend singular optics beyond isolated phase and polarization defects to particle-like textures distributed throughout a finite propagation volume. Optical hopfions are a prominent example, characterized by linked polarization preimages and a nontrivial phase–polarization mapping onto the optical hypersphere. However, their experimental realization has so far relied on bulky, alignment-sensitive optical systems. Here, we introduce for the first time a compact platform for the generation and continuous reconfiguration of optical hopfions using a single dual-functional metasurface. The device independently controls the right- and left-circular polarization channels, encoding optimized modal amplitudes through phase equalization, and simultaneously providing the focusing phase required for volumetric field synthesis. The input ellipticity is fixed to establish the relative spin-channel weights and generate the target hopfion at focus, while reconfiguration is achieved simply by rotating the input polarization ellipse. We experimentally reconstruct the three-dimensional polarization Hopf fibrations associated with generalized (m, n) = (1, −1) and (1, 2) textures, while full-field propagation simulations reveal localized signed Skyrme densities with integrated degrees of 0.99 and −1.99, respectively. By integrating spin-decoupled control, amplitude equalization, and focusing within a single flat optical element, our approach provides a practical and scalable route to reconfigurable particle-like topological light and its application in optics and photonics.
Sensitive terahertz (THz) detectors are essential for all THz applications. The recently unveiled in-plane photoelectric effect is a novel, quantum mechanism enabling terahertz detection with high responsivities in 2D electron gases (2DEGs). Here, we investigate the influence of transverse confinement in 2DEGs on the in-plane photoelectric response by measuring AlGaAs/GaAs-based photoelectric tunable-step THz detectors with symmetric antennas but different shapes of the underlying 2DEG. Despite fully symmetric antennas, the geometric channel asymmetry notably shifts the gate voltage dependence of the photoresponse. Our findings underscore the highly localized nature of the in-plane photoelectric effect as a quantum photodetection mechanism. The results show how tailored shapes of 2DEG channels influence the quantum-mechanical photocurrent arising along the electron channel direction by modifying the number of subbands corresponding to electron motion perpendicular to the channel. Our work shows that quantum effects influence photodetection phenomena not only along the direction of electron flow but also in the transverse, perpendicular direction—even in degenerate 2DEGs and on length scales of several microns. This provides a path to structural engineering of quantum light–matter interactions in 2DEGs.
We report a combined experimental and theoretical study of enhanced third-harmonic generation from silicon nitride (Si3N4) metasurfaces, where enhanced deep-UV emission is enabled by a phase locking mechanism between the pump and the generated harmonics. In wide-bandgap dielectrics, the linear response at the harmonic wavelength is strongly absorbing, which would normally suppress third-harmonic generation (THG). However, the nonlinear polarization acts as an inhomogeneous source term in Maxwell’s equations, generating a phase-locked third-harmonic field that inherits the dispersion and propagation characteristics of the pump rather than those of the material at the harmonic frequency. As a result, the inhomogeneous solution propagates through the Si3N4 membrane without experiencing the deep-UV absorption that governs the homogeneous solution. We experimentally verify this inhibition of absorption by measuring absolute THG conversion efficiencies down to the 10−9–10−10 level at ∼266 nm, enabled by a fully calibrated deep-UV detection system. Two metasurface geometries, a guided-mode resonance grating and a fully suspended Mie-type grating, provide strong pump-field localization, yielding nearly two orders of magnitude enhancement relative to a flat membrane. By combining diffraction-resolved third-harmonic generation measurements with a hydrodynamic-Maxwell model that incorporates both linear and nonlinear dispersion, we retrieve the wavelength-dependent χ(3) of Si3N4 and demonstrate how resonant field confinement synergistically amplifies the phase-locked nonlinear response. These results establish Si3N4 as a CMOS-compatible platform for efficient deep-UV frequency conversion and highlight phase locking as a powerful mechanism for overcoming intrinsic material absorption in nonlinear nanophotonics.
