Reflective displays, which harness ambient light, offer energy-efficient alternatives to traditional emissive screens in mobile devices. This review provides an overview of various reflective display technologies and their comparative performance metrics. The review highlights the potential of micro-electromechanical system-based displays, with metrics including 90% reflectance, a contrast ratio of 30, a frequency of 120 Hz, and a resolution of about 350 pixels per inch. Their applicability to mainstream devices such as e-readers, smartphones, and smartwatches continues to be a topic of interest and exploration.

We review progress in the development of photonic platforms for detecting gases. Unlike sensors based on conventional refractive and diffractive optics, photonic sensors detect analytes using light–matter interactions of periodic nanostructures, plasmonic interactions, or combinations of the two. This summary focuses on the work done in the last two decades, and earlier reports are summarized in several authoritative reviews. Specifically, we focus on the research of bio-inspired photonic and plasmonic material fabrication, experimental studies, and theoretical studies for gas detection applications. In areas where reports are scarce, challenges are identified, and reports are included that may not directly relate to bio-inspired gas detection applications but nonetheless offer findings that can facilitate progress within underexplored areas of bioinspired gas sensing.

Spectroscopy has emerged as an essential technology, particularly in decentralized utilization within point-of-care devices. These applications demand compact, cost-effective designs with reduced complexity compared with traditional laboratory equipment. Achieving compactness often involves minimizing the number of components, necessitating that each remaining component fulfills multiple functions to optimize performance. However, this approach can lead to significant aberrations due to constructive compromises. Nevertheless, the known phase errors enable correction, often achieved directly through diffractive elements. Diffractive compensation of aberrations is commonly conducted through interference lithography, exploiting holographic techniques to produce gratings without explicit knowledge of the interference structure. Alternatively, mechanical manufacturing techniques offer the possibility of producing blazed gratings with greater efficiency. However, diffractive correction using mechanically fabricated gratings requires a precise understanding of individual groove trajectories, presenting an ongoing challenge. We employed ultraprecision (UP) mechanical manufacturing techniques to create aberration-corrected diffraction gratings for spectroscopic applications. To enable the machining of freeform trajectories, facilitating versatile fabrication of both planar and concave imaging blazed gratings, a modified five-axis UP machinery is employed. To correct the known wavefront errors of the exemplary use cases, a nonlinear phase function was applied and a numerical method was developed to derive trajectories from the phase errors and translate them into machine code. The use cases are a blazed imaging planar Littrow grating and concave Rowland gratings, showcasing corrected astigmatic wavefront deviation. The theoretical and experimental results are compared and discussed.

Additive manufacturing of microoptics using two-photon-lithography has been a rapidly advancing field of technology. Striving for ever more sophisticated optical systems prerequisites the access to appropriately fast and accurate wave-optical simulation methods to predict their optical performance. A simulation routine, which has been proven well suited for simulation of a vast range of 3D-printed microoptical systems, is the wave propagation method (WPM). Nevertheless, limitations in applicability remain due to the restriction on scalar electromagnetic fields, which prohibits consideration of polarization and thereby also the calculation of backward reflection at optical interfaces. Capabilities for design and analyses are, therefore, impaired for 3D-printed optical systems using those properties as key features in their design. As a first step to overcome those limitations, we presented new simulation methods based on the WPM in previous publications, extending its applicability toward simulation of vector electric fields, while maintaining short-simulation runtime. We focus on elaborating the practical application and integration of previously presented simulation methods in the design of complex 3D-printed optical systems. With it, we demonstrate the consideration of polarization and backward reflections in simulations far beyond paraxial and thin element approximations.

We demonstrate a microwave photonic spectrometer based on laser speckle pattern imaging that has some significant advantages over state-of-the-art electronic technology, including high resolution, multifrequency detection over broad and reconfigurable bandwidths. The spectrometer operates by modulating the radio-frequency (RF) signal on a frequency-stabilized continuous wave (CW) laser using an electro-optic intensity modulator. The modulated CW laser travels through a 100-m long high numerical aperture multimode optical fiber before collection and recording on a camera. To calibrate the spectrometer, an RF tone generator is stepped over the desired operational range of the spectrometer with a frequency step size on the order of the desired frequency resolution while the speckle pattern images are recorded and stored. An unknown signal under test is then generated and recovered from the calibration set using regression analysis techniques. The spectrometer exhibits a 5-MHz resolution with a single-tone recovery accuracy of greater than 99.9% over a 17-GHz frequency range and a mean recovery error below 1 MHz over smaller ranges. We also incorporated a high-speed camera, operated at an 800-kHz frame rate, permitting data collection at speeds commensurate with the best real-time spectrum analyzers. We present the results of our analysis of the spectrum recovery process with the goal of increasing the spectral recovery rate. In addition, in the interest of miniaturization, we present the results of simulations of 50-μm wide and 40-cm long multimode waveguides in silicon nitride and silicon, which suggest that the 100-m long multimode fiber can be replaced by short waveguides without degradation in performance.