APL Photonics, Volume 8, Issue 4, April 2023. A Mach–Zehnder interferometer is a basic building block for linear transformations that has been widely applied in optical neural networks. However, its sinusoidal transfer function leads to the inevitable dynamic phase quantization error, which is hard to eliminate through pre-calibration. Here, a strongly overcoupled ring is introduced to compensate for the phase change without adding perceptible loss. Two full-scale linearized Mach–Zehnder interferometers are proposed and experimentally validated to improve the bit precision from 4-bit to 6- and ..read more

APL Photonics, Volume 8, Issue 4, April 2023. Visible light optical coherence tomography (vis-OCT) provides a unique tool for imaging both structure and oxygen metabolism in ophthalmology. Working in visible light bandwidth, it suffers from noises due to strong scattering, especially in the blood. This work established the random matrix (RM) description of vis-OCT’s k-space data as ballistic and multiple scattering components. The eigenvalue density of the hybrid RM follows a low-rank biased Marčenko–Pastur law. The ballistic component can thus be separated out using a generalized likelihood r ..read more

APL Photonics, Volume 8, Issue 4, April 2023. Multispectral imaging and time-resolved imaging are two common acquisition schemes in fluorescence microscopy, and their combination can be beneficial to increase specificity. The multidimensionality of the dataset (space, time, and spectrum) introduces some challenges, such as the acquisition of big datasets and long measurement times. In this work, we present a time-resolved multispectral fluorescence microscopy system with a short measurement time, achieved by exploiting Compressive Sensing (CS) based on the Single-Pixel Camera (SPC) scheme. Dat ..read more

APL Photonics, Volume 8, Issue 4, April 2023. Spectral sensing is an emerging field driven by the need for fast and non-invasive methods for the chemical analysis of materials in agri-food, healthcare, and industrial applications. We demonstrate a near-infrared spectral sensor, based on a scalable fabrication process and combining high responsivity, narrow linewidth, and low noise. The sensor consists of 16 resonant-cavity-enhanced photodetectors, each showing a unique spectral response consisting of narrow peaks. The spectral sensor thereby covers the wavelength range between 890 and 1650&nbs ..read more

APL Photonics, Volume 8, Issue 4, April 2023. The advent of topological semi-metals with peculiar band structure and exotic quantum-transport provides novel pathways for upgrading the performance of terahertz (THz) detection. HgTe is among such a candidate with the unique advantages of a negative bandgap, ultra-high mobility, and thermoelectricity, which ignites the possibility of addressing the technical bottlenecks of traditional routes for THz detection. Herein, for the first time, we report large-area (3 in.) growth of high-mobility HgTe thin-film via molecular-beam epitaxial and the imple ..read more

APL Photonics, Volume 8, Issue 4, April 2023. We report experimental observations and numerical simulations of second and third harmonic generation from a gold nanograting, which exhibits a plasmonic resonance in the near infrared. The resonance is tunable, with a spectral position that depends on the angle of incidence. All things being equal, the enhancement of nonlinear optical processes produced by the field localization in the nanograting when compared with a flat gold mirror manifests itself dramatically from the ultraviolet to the visible range: second harmonic generation conversion eff ..read more

APL Photonics, Volume 8, Issue 4, April 2023. Open-access microcavities are a powerful tool to enhance light–matter interactions for solid-state quantum and nanosystems and are key to advance applications in quantum technologies. For this purpose, the cavities should simultaneously meet two conflicting requirements—full tunability to cope with spatial and spectral inhomogeneities of a material and highest stability under operation in a cryogenic environment to maintain resonance conditions. To tackle this challenge, we have developed a fully tunable, open-access, fiber-based Fabry–Pérot microc ..read more

APL Photonics, Volume 8, Issue 4, April 2023. Exciton–polaritons in optical cavities exhibit strong nonlinearities predominantly because of the third-order Kerr-like interactions mediated by the excitonic component. Under quasi-resonant excitation, depending on the energy of the incident laser, it results in the optical limiting or bistable behavior. The latter phenomenon is manifested by the hysteresis loop observed in the input–output power characteristics, when a cavity is quasi-resonantly driven by a laser field. The direction of the loop is typically counterclockwise when increasing and s ..read more

APL Photonics, Volume 8, Issue 4, April 2023. Masked Autoencoders (MAEs), the state-of-the-art self-supervised neural network architecture in miscellaneous vision tasks, show surprisingly effective potential in reconstructing images distorted by random masking. This paper first introduces an optical implementation of MAEs, employing digital micromirror devices in the optical path to capture partially blocked images. MAEs with multi-scale patches are deployed in the reconstruction procedure. By using an optical-specialized version of the reconstruction network, the system can reconstruct origin ..read more

APL Photonics, Volume 8, Issue 4, April 2023. We propose and demonstrate a silicon photonic integrated circuit (PIC) for exciting different spatial modes launched into a multimode-fiber (MMF) speckle imaging system. The PIC consists of a 45-channel optical phased array and an array of nanoantennas to bridge the PIC and MMF. The nanoantenna array can excite a wide range of spatial modes in the MMF with a mode-group dependent loss of less than 3 dB. A high spatial resolution, which approaches the theoretical limit determined by the number of modes in the MMF, is realized by using the proposed PI ..read more