In article number 2100057, John E. Bowers, Yating Wan, Chao Xiang, and co-workers report record-setting quantum dot (QD) distributed feedback lasers on Si with a 3-dB modulation bandwidth of 13 GHz, a threshold current of 4 mA, a side-mode-suppression-ratio of 60 dB, and a fundamental linewidth of 26 kHz. The broadband QD lasers and the Si-on-insulator waveguiding platform can be expanded to build fully functional photonic integrated circuits throughout the O band.

In article number 2100072, Feng Tian, Junjie Hu, and Weijian Yang demonstrate GEOMScope, a lensless microscope that can image 3D objects over a large volume with fine resolution. GEOMScope forms images through a thin layer of random microlens arrays, and reconstructs the 3D objects through an innovative, highly efficient algorithm combining geometrical optics and machine learning. This algorithm requires minimal computational resources and enables high-resolution, real-time 3D imaging over a large volume.

In article number 2000584, Tao Li and co-workers from Nanjing University experimentally demonstrated topological π modes induced by Floquet gauge transition in a silicon waveguides platform. The flexible control of the Floquet gauge provides new degrees of freedom to manipulate the topological modes and enables interesting functionalities such as asymmetric topological transport, i.e., the localization is protected only for light propagating in one direction.

In article number 2000441, Maciej Kowalczyk and co-workers developed a novel technique for simultaneous generation of two pulse trains from a single femtosecond laser. It is based on polarization-multiplexing in a birefringent gain medium and allowed to achieve the lowest relative noise ever demonstrated for any solid-state dual-comb laser. This simple technique can be utilized for free-running, but yet very precise spectroscopic measurements.

Optical dielectric metasurfaces composed of arrayed nanoresonators, often called Huygens' metasurfaces, offer excellent performance for periodic arrays. However, when a gradual variation of the resonator sizes is implemented, performance is quite degraded. There are profound reasons for this degradation. We clarify them based on general arguments, such as reciprocity, multimode-versus-monomode operation and symmetry breaking.

This review addresses a key question: how to overcome the acoustic resolution barrier of photoacoustic (PA)-guided wavefront shaping (WFS)? In particular, this paper provides rules that govern the optical focusing efficiency of PA-guided WFS in the frequency domain, the time domain, and the spatial domain. These summarized rules and findings will facilitate further breakthroughs in PA-guided WFS.

An electrically powered on-chip mode-locked laser consisting of a silicon-nitride waveguide cavity and a heterogeneously integrated amplifier and saturable absorber is demonstrated. A narrow 755 MHz comb-line spacing, a radio frequency linewidth of 1 Hz and an optical linewidth below 200 kHz are achieved. Moreover, these optical comb sources are fabricated with wafer scale technology.

In this work, it is demonstrated that a single resonant nanoparticle placed above a substrate and illuminated with a focused beam containing only propagating far-field components can perfectly absorb all the incident energy without scattering it back.

A novel class of nanojunctions are developed which demonstrate directed electron currents optically controllable at the time scale of tens and hundreds of femtoseconds, which work at room temperature and independently to the carrier-envelope phase of the pump. We show the leading role of inter-cycle quantum-mechanical interference of the electronic wavepackets in the buildup of the current is shown.

A novel scheme for simultaneous generation of two pulse trains from a single femtosecond laser is demonstrated. It is based on intrinsic polarization-multiplexing in a birefringent gain medium and allowed achieving the lowest relative noise ever demonstrated for any solid-state dual-comb laser. This simple technique can be used for free-running yet very precise spectroscopic measurements.

In this study, an architecture of a wavelength-division-multiplexing-based electronic–photonic digital comparator is proposed, which can perform high-bit comparisons for fixed-point or floating-point binary inputs. A high-speed silicon photonics-based 2-bit comparator operating at a 1.55 µm wavelength is experimentally demonstrated. This architecture outperforms the current transistor-based electronic comparators in terms of computational speed and power efficiency.

Conventional digital holographic particle tracking velocimetry techniques are computationally separated in particle and flow reconstruction. Single-shot space–time holographic particle tracking velocimetry is demonstrated using a customized joint optimization algorithm efficiently runs on a GPU to achieve particle-flow joint reconstruction, demonstrating improved particle quality.

A chemical doping method is demonstrated for graphene/Si photodetectors. Upon doping, the dark current reduced by three orders of magnitude from 980 nA to 219 pA and detectivity improved by 529% at 850 nm. This doping process can be easily conducted at a large scale at a low cost and may be extended to different applications.

Room temperature polariton lasing is demonstrated in two fluorene-based oligomers at record low absorbed thresholds of 3.3 and 2.2 µJ cm⁻². By combining favorable material properties and optimal microcavity configuration, this work brings the polariton lasing threshold down to the typical order of magnitude for organic photon lasers and paves the way to realization of electrically driven polariton lasers.

Femtosecond laser irradiation of single-crystal halide perovskite CsPbBr₃ allows for its precise and ultraclean ablation fully controlled at subwavelength scale by the intensity and polarization distribution of the complex laser field applied. The direct imprinting of the incident laser field results in the creation of micro-lens and various light-emitting metasurfaces with deeply subwavelength spatial resolution (down to lambda/7).

A compact polarization imaging apparatus that leverages a multifunctional planar dielectric metalens to simultaneously capture two orthogonally polarized images of an underwater scene is presented. Using a metalens to image target objects through milky water in a single shot, large enhancement of image contrast and depth estimation of target objects in real-time are demonstrated.

On-chip light amplification with integrated optical waveguide fabricated on erbium-doped thin-film lithium niobate on insulator (TFLNOI) is demonstrated using the photolithography-assisted chemomechanical etching (PLACE) technique. A maximum internal net gain of 18 dB is measured on a waveguide length of 3.6 cm, indicating a differential gain per unit length of 5 dB cm⁻¹.

Direct laser writing with increased resolution, never reached for liquid crystalline networks, is demonstrated at controlled polymerization temperatures. A careful voxel shape analysis demonstrates that temperature, swelling, and molecular anisotropy rule the 3D polymerizable unit dimension. The resulting voxel, now comparable with the typical one of commercial resists, enlarges the application field of responsive polymers without degradation of the structure rigidity.

Record-setting quantum dot (QD) distributed feedback lasers on Si are reported, with a 3-dB modulation bandwidth of 13 GHz, a threshold current of 4 mA, a side-mode-suppression-ratio of 60 dB, and a fundamental linewidth of 26 kHz. The broadband QD lasers and the Si-on-insulator waveguiding platform can be expanded to build fully functional photonic integrated circuits throughout the O band.

A lensless single-shot 3D microscope which forms image through a single layer of thin microlens array is demonstrated. The imager reconstructs objects by an innovative hybrid algorithm developed through a joint application of geometrical optics and machine learning. The algorithm requires minimal computational resources and enables real-time 3D high-resolution imaging over a large field of view.

The ever-increasing demand for higher bandwidths in wireless communications systems and ultrahigh speed signal processing operations has pushed state-of-the-art technologies to operate at terahertz (THz) frequencies. Such new platforms urgently require the development of fundamental building blocks, enabling wideband performance. Here, a time-domain integrator device for broadband THz pulses, relying on a tapered two-wire waveguide, is demonstrated.

The gauge-induced topological state localized at the interface between two gauge-shifted Floquet photonic lattices with the same topological order, which are further found to enable an asymmetric topological transport with broadband working wavelengths and robustness against the structural fluctuations, is demonstrated. The results will open a new avenue in manipulating optical topological modes and in assembling on-chip topological optical devices.